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5957 lines
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<title>
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HDF5 File Format Specification
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* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
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* Copyright by the Board of Trustees of the University of Illinois. *
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* All rights reserved. *
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* *
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* This file is part of HDF5. The full HDF5 copyright notice, including *
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* terms governing use, modification, and redistribution, is contained in *
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* the files COPYING and Copyright.html. COPYING can be found at the root *
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* of the source code distribution tree; Copyright.html can be found at the *
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* root level of an installed copy of the electronic HDF5 document set and *
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* is linked from the top-level documents page. It can also be found at *
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* http://hdf.ncsa.uiuc.edu/HDF5/doc/Copyright.html. If you do not have *
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<!-- #BeginLibraryItem "/ed_libs/NavBar_ADevG.lbi" --><hr>
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<center>
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<table border=0 width=98%>
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<tr><td valign=top align=left>
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<a href="index.html">HDF5 documents and links</a> <br>
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<a href="H5.intro.html">Introduction to HDF5</a> <br>
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<!--
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<a href="Glossary.html">Glossary</a><br>
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-->
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</td>
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<td valign=top align=right>
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<a href="http://hdf.ncsa.uiuc.edu/HDF5/doc/UG/index.html">HDF5 User's Guide</a> <br>
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<a href="RM_H5Front.html">HDF5 Reference Manual</a> <br>
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<a href="ADGuide.html">HDF5 Application Developer's Guide</a> <br>
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</td></tr>
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</table>
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</center>
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<hr>
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<!-- #EndLibraryItem --><center><h1>HDF5 File Format Specification</h1></center>
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<center>
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<table border=0 width=90%>
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<tr>
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<td valign=top>
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<ol type=I>
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<li><a href="#Intro">Introduction</a>
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<li><a href="#FileMetaData">Disk Format Level 0 - File Metadata</a>
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<font size=-2>
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<ol type=A>
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<li><a href="#SuperBlock">Disk Format Level 0A - File Signature and Super Block</a>
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<li><a href="#DriverInfo">Disk Format Level 0B - File Driver Info</a>
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</ol>
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</font>
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<li><a href="#FileInfra">Disk Format Level 1 - File Infrastructure</a>
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<font size=-2>
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<ol type=A>
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<li><a href="#Btrees">Disk Format Level 1A - B-link Trees and B-tree Nodes</a>
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<li><a href="#SymbolTable">Disk Format Level 1B - Group</a>
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<li><a href="#SymbolTableEntry">Disk Format Level 1C - Group Entry</a>
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<li><a href="#LocalHeap">Disk Format Level 1D - Local Heaps</a>
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<li><a href="#GlobalHeap">Disk Format Level 1E - Global Heap</a>
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<li><a href="#FreeSpaceIndex">Disk Format Level 1F - Free-space Index</a>
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</ol>
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</font>
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<li><a href="#DataObject">Disk Format Level 2 - Data Objects</a>
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<font size=-2>
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<ol type=A>
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<li><a href="#ObjectHeader">Disk Format Level 2a - Data Object Headers</a>
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<ol type=1>
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<li><a href="#NILMessage">Name: NIL</a> <!-- 0x0000 -->
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<li><a href="#SimpleDataSpace">Name: Simple Dataspace</a> <!-- 0x0001 -->
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<!-- <li><a href="#DataSpaceMessage">Name: Complex Dataspace</a> --> <!-- 0x0002 -->
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<li><a href="#ReservedMessage_0002">Name: Reserved - not assigned yet</a> <!-- 0x0002 -->
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<li><a href="#DataTypeMessage">Name: Datatype</a> <!-- 0x0003 -->
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<li><a href="#OldFillValueMessage">Name: Data Storage - Fill Value (Old)</a> <!-- 0x0004 -->
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<li><a href="#FillValueMessage">Name: Data Storage - Fill Value</a> <!-- 0x0005 -->
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</ol>
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</ol>
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</font>
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</ol>
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</td><td> </td><td valign=top>
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<ol type=I start=4>
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<li><a href="#DataObject">Disk Format Level 2 - Data Objects</a>
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<font size=-2><i>(Continued)</i>
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<ol type=A>
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<li><a href="#ObjectHeader">Disk Format Level 2a - Data Object Headers</a><i>(Continued)</i>
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<ol type=1 start=6>
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<!-- <li><a href="#CompactDataStorageMessage">Name: Data Storage - Compact</a> --> <!-- 0x0006 -->
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<li><a href="#ReservedMessage_0006">Name: Reserved - not assigned yet</a> <!-- 0x0006 -->
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<li><a href="#ExternalFileListMessage">Name: Data Storage - External Data Files</a> <!-- 0x0007 -->
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<li><a href="#LayoutMessage">Name: Data Storage - Layout</a> <!-- 0x0008 -->
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<li><a href="#ReservedMessage_0009">Name: Reserved - not assigned yet</a> <!-- 0x0009 -->
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<li><a href="#ReservedMessage_000A">Name: Reserved - not assigned yet</a> <!-- 0x000a -->
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<li><a href="#FilterMessage">Name: Data Storage - Filter Pipeline</a> <!-- 0x000b -->
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<li><a href="#AttributeMessage">Name: Attribute</a> <!-- 0x000c -->
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<li><a href="#CommentMessage">Name: Object Comment</a> <!-- 0x000d -->
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<li><a href="#OldModifiedMessage">Name: Object Modification Date and Time (Old)</a> <!-- 0x000e -->
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<li><a href="#SharedMessage">Name: Shared Object Message</a> <!-- 0x000f -->
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<li><a href="#ContinuationMessage">Name: Object Header Continuation</a> <!-- 0x0010 -->
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<li><a href="#SymbolTableMessage">Name: Group Message</a> <!-- 0x0011 -->
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<li><a href="#ModifiedMessage">Name: Object Modification Date and Time</a> <!-- 0x0012 -->
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</ol>
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<li><a href="#SharedObjectHeader">Disk Format: Level 2b - Shared Data Object Headers</a>
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<li><a href="#DataStorage">Disk Format: Level 2c - Data Object Data Storage</a>
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</ol>
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</font>
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<LI><A href="#Appendix">Appendix</A>
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</ol>
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</td></tr>
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</table>
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</center>
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<BR>
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<HR>
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<h2>Introduction</h2>
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<table align=right width=100>
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<tr><td> </td><td align=center>
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<hr>
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<img src="FF-IH_FileGroup.gif" alt="HDF5 Groups" hspace=15 vspace=15>
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</td><td> </td></tr>
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<tr><td> </td><td align=center>
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<strong>Figure 1:</strong> Relationships among the HDF5 root group, other groups, and objects
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<hr>
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</td><td> </td></tr>
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<tr><td> </td><td align=center>
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<img src="FF-IH_FileObject.gif" alt="HDF5 Objects" hspace=15 vspace=15>
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</td><td> </td></tr>
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<tr><td> </td><td align=center>
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<strong>Figure 2:</strong> HDF5 objects -- datasets, datatypes, or dataspaces
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<hr>
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</td><td> </td></tr>
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</table>
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<P>The format of an HDF5 file on disk encompasses several
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key ideas of the HDF4 and AIO file formats as well as
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addressing some shortcomings therein. The new format is
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more self-describing than the HDF4 format and is more
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uniformly applied to data objects in the file.
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<P>An HDF5 file appears to the user as a directed graph.
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The nodes of this graph are the higher-level HDF5 objects
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that are exposed by the HDF5 APIs:
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<ul>
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<li>Groups
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<li>Datasets
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<li>Named datatypes
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</ul>
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<P>At the lowest level, as information is actually written to the disk,
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an HDF5 file is made up of the following objects:
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<ul>
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<li>A super block
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<li>B-tree nodes (containing either symbol nodes or raw data chunks)
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<li>Object headers
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<li>A global heap
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<li>Local heaps
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<li>Free space
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</ul>
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<P>The HDF5 library uses these low-level objects to represent the
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higher-level objects that are then presented to the user or
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to applications through the APIs.
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For instance, a group is an object header that contains a message that
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points to a local heap and to a B-tree which points to symbol nodes.
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A dataset is an object header that contains messages that describe
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datatype, space, layout, filters, external files, fill value, etc
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with the layout message pointing to either a raw data chunk or to a
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B-tree that points to raw data chunks.
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<h3>This Document</h3>
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<p>This document describes the lower-level data objects;
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the higher-level objects and their properties are described
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in the <a href="H5.user.html"><cite>HDF5 User's Guide</cite></a>.
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<P>Three levels of information comprise the file format.
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Level 0 contains basic information for identifying and
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defining information about the file. Level 1 information contains
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the information about the pieces of a file shared by many objects
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in the file (such as a B-trees and heaps). Level 2 is the rest
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of the file and contains all of the data objects, with each object
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partitioned into header information, also known as
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<em>metadata</em>, and data.
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<p>The sizes of various fields in the following layout tables are
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determined by looking at the number of columns the field spans
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in the table. There are three exceptions: (1) The size may be
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overridden by specifying a size in parentheses, (2) the size of
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|
addresses is determined by the <em>Size of Offsets</em> field
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|
in the super block and is indicated in this document with a
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superscripted 'O', and (3) the size of length fields is determined
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by the <em>Size of Lengths</em> field in the super block and is
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indicated in this document with a superscripted 'L'.
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<P>Values for all fields in this document should be treated as unsigned
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integers, unless otherwise noted in the description of a field.
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Additionally, all metadata fields are stored in little-endian byte
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order.
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</P>
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<BR>
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<HR>
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<h2><a name="FileMetaData">
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Disk Format: Level 0 - File Metadata</a></h2>
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<H3><A name="SuperBlock">
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Disk Format: Level 0A - File Signature and Super Block</A></H3>
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<P>The super block may begin at certain predefined offsets within
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the HDF5 file, allowing a block of unspecified content for
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|
users to place additional information at the beginning (and
|
|
end) of the HDF5 file without limiting the HDF5 library's
|
|
ability to manage the objects within the file itself. This
|
|
feature was designed to accommodate wrapping an HDF5 file in
|
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another file format or adding descriptive information to the
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file without requiring the modification of the actual file's
|
|
information. The super block is located by searching for the
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HDF5 file signature at byte offset 0, byte offset 512 and at
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successive locations in the file, each a multiple of two of
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the previous location, i.e. 0, 512, 1024, 2048, etc.
|
|
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<P>The super block is composed of a file signature, followed by
|
|
super block and group version numbers, information
|
|
about the sizes of offset and length values used to describe
|
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items within the file, the size of each group page,
|
|
and a group entry for the root object in the file.
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<br>
|
|
<div align=center>
|
|
<table class=format>
|
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<caption>
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|
HDF5 Super Block Layout
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</caption>
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<tr>
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<th>byte</th>
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<th>byte</th>
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<th>byte</th>
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<th>byte</th>
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</tr>
|
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<tr>
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<td colspan=4><br>HDF5 File Signature (8 bytes)<br><br></td>
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</tr>
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<tr>
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<td>Version # of Super Block</td>
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<td>Version # of Global Free-space Storage</td>
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<td>Version # of Root Group Symbol Table Entry</td>
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<td>Reserved (zero)</td>
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</tr>
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<tr>
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<td>Version # of Shared Header Message Format</td>
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<td>Size of Offsets</td>
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<td>Size of Lengths</td>
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<td>Reserved (zero)</td>
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</tr>
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<tr>
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<td colspan=2>Group Leaf Node K</td>
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<td colspan=2>Group Internal Node K</td>
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</tr>
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<tr>
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<td colspan=4>File Consistency Flags</td>
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</tr>
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<tr>
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<td colspan=2 style="border:dotted;">Indexed Storage Internal Node K<sup>1</sup></td>
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<td colspan=2 style="border:dotted;">Reserved (zero)<sup>1</sup></td>
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</tr>
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<tr>
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<td colspan=4>Base Address<sup>O</sup></td>
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</tr>
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<tr>
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<td colspan=4>Address of Global Free-space Heap<sup>O</sup></td>
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</tr>
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<tr>
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<td colspan=4>End of File Address<sup>O</sup></td>
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</tr>
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<tr>
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<td colspan=4>Driver Information Block Address<sup>O</sup></td>
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</tr>
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<tr>
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<td colspan=4>Root Group Symbol Table Entry</td>
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</tr>
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</table>
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<table class=note>
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<tr><td>
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(Items marked with an 'O' the above table are
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<br>
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of the size specified in "Size of Offsets.")
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</td></tr>
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<tr><td>
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(Items marked with an '1' the above table are
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<br>
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new in version 1 of the superblock)
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</td></tr>
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</table>
|
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</div>
|
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<br>
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<div align=center>
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|
<table class=desc>
|
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<tr>
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<th width="30%">Field Name</th>
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<th>Description</th>
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</tr>
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<tr>
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<td>HDF5 File Signature</td>
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<td>
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<P>This field contains a constant value and can be used to
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quickly identify a file as being an HDF5 file. The
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|
constant value is designed to allow easy identification of
|
|
an HDF5 file and to allow certain types of data corruption
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to be detected. The file signature of an HDF5 file always
|
|
contains the following values:
|
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</P>
|
|
|
|
<center>
|
|
<table border align=center cellpadding=4>
|
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<tr align=center>
|
|
<td align=right>Decimal:</td>
|
|
<td width="8%">137</td>
|
|
<td width="8%">72</td>
|
|
<td width="8%">68</td>
|
|
<td width="8%">70</td>
|
|
<td width="8%">13</td>
|
|
<td width="8%">10</td>
|
|
<td width="8%">26</td>
|
|
<td width="8%">10</td>
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</tr>
|
|
|
|
<tr align=center>
|
|
<td align=right>Hexadecimal:</td>
|
|
<td>89</td>
|
|
<td>48</td>
|
|
<td>44</td>
|
|
<td>46</td>
|
|
<td>0d</td>
|
|
<td>0a</td>
|
|
<td>1a</td>
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|
<td>0a</td>
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|
</tr>
|
|
|
|
<tr align=center>
|
|
<td align=right>ASCII C Notation:</td>
|
|
<td>\211</td>
|
|
<td>H</td>
|
|
<td>D</td>
|
|
<td>F</td>
|
|
<td>\r</td>
|
|
<td>\n</td>
|
|
<td>\032</td>
|
|
<td>\n</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
<br>
|
|
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|
<P>This signature both identifies the file as an HDF5 file
|
|
and provides for immediate detection of common
|
|
file-transfer problems. The first two bytes distinguish
|
|
HDF5 files on systems that expect the first two bytes to
|
|
identify the file type uniquely. The first byte is
|
|
chosen as a non-ASCII value to reduce the probability
|
|
that a text file may be misrecognized as an HDF5 file;
|
|
also, it catches bad file transfers that clear bit
|
|
7. Bytes two through four name the format. The CR-LF
|
|
sequence catches bad file transfers that alter newline
|
|
sequences. The control-Z character stops file display
|
|
under MS-DOS. The final line feed checks for the inverse
|
|
of the CR-LF translation problem. (This is a direct
|
|
descendent of the <A href="http://www.libpng.org/pub/png/spec/PNG-Rationale.html#R.PNG-file-signature">PNG</A> file
|
|
signature.)
|
|
</P>
|
|
|
|
<P><EM>This field is present in version 0+ of the superblock.</EM>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Version Number of the Super Block</td>
|
|
<td>
|
|
<P>This value is used to determine the format of the
|
|
information in the super block. When the format of the
|
|
information in the super block is changed, the version number
|
|
is incremented to the next integer and can be used to
|
|
determine how the information in the super block is
|
|
formatted.
|
|
</P>
|
|
|
|
<P>Values of 0 and 1 are defined for this field.
|
|
</P>
|
|
|
|
<P><EM>This field is present in version 0+ of the superblock.</EM>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Version Number of the File Free-space Information</td>
|
|
<td>
|
|
<P>This value is used to determine the format of the
|
|
information in the File Free-space Information.
|
|
</P>
|
|
<P>The only value currently valid in this field is '0', which
|
|
indicates that the free space index is formatted as described
|
|
<A href="#FreeSpaceIndex">below</A>.
|
|
</P>
|
|
|
|
<P><EM>This field is present in version 0+ of the superblock.</EM>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Version Number of the Root Group Symbol Table Entry</td>
|
|
<td>
|
|
<P>This value is used to determine the format of the
|
|
information in the Root Group Symbol Table Entry. When the
|
|
format of the information in that field is changed, the
|
|
version number is incremented to the next integer and can be
|
|
used to determine how the information in the field
|
|
is formatted.
|
|
</P>
|
|
<P>The only value currently valid in this field is '0', which
|
|
indicates that the root group symbol table entry is formatted as
|
|
described <A href="#SymbolTableEntry">below</A>.
|
|
</P>
|
|
|
|
<P><EM>This field is present in version 0+ of the superblock.</EM>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Version Number of the Shared Header Message Format</td>
|
|
<td>
|
|
<P>This value is used to determine the format of the
|
|
information in a shared object header message, which is
|
|
stored in the global small-data heap. Since the format
|
|
of the shared header messages differs from the private
|
|
header messages, a version number is used to identify changes
|
|
in the format.
|
|
</P>
|
|
<P>The only value currently valid in this field is '0', which
|
|
indicates that shared header messages are formatted as
|
|
described <A href="#SharedObjectHeader">below</A>.
|
|
</P>
|
|
|
|
<P><EM>This field is present in version 0+ of the superblock.</EM>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Size of Offsets</td>
|
|
<td>
|
|
<P>This value contains the number of bytes used to store
|
|
addresses in the file. The values for the addresses of
|
|
objects in the file are offsets relative to a base address,
|
|
usually the address of the super block signature. This
|
|
allows a wrapper to be added after the file is created
|
|
without invalidating the internal offset locations.
|
|
</P>
|
|
|
|
<P><EM>This field is present in version 0+ of the superblock.</EM>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Size of Lengths</td>
|
|
<td>
|
|
<P>This value contains the number of bytes used to store
|
|
the size of an object.
|
|
</P>
|
|
|
|
<P><EM>This field is present in version 0+ of the superblock.</EM>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Group Leaf Node K</td>
|
|
<td>
|
|
<P>Each leaf node of a group B-tree will have at
|
|
least this many entries but not more than twice this
|
|
many. If a group has a single leaf node then it
|
|
may have fewer entries.
|
|
</P>
|
|
<P>This value must be greater than zero.
|
|
</P>
|
|
<P>See the <A href="#Btrees">description</A> of B-trees below.
|
|
</P>
|
|
|
|
<P><EM>This field is present in version 0+ of the superblock.</EM>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Group Internal Node K</td>
|
|
<td>
|
|
<P>Each internal node of a group B-tree will have at
|
|
least this many entries but not more than twice this
|
|
many. If the group has only one internal
|
|
node then it might have fewer entries.
|
|
</P>
|
|
<P>This value must be greater than zero.
|
|
</P>
|
|
<P>See the <A href="#Btrees">description</A> of B-trees below.
|
|
</P>
|
|
|
|
<P><EM>This field is present in version 0+ of the superblock.</EM>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>File Consistency Flags</td>
|
|
<td>
|
|
<P>This value contains flags to indicate information
|
|
about the consistency of the information contained
|
|
within the file. Currently, the following bit flags are
|
|
defined:
|
|
<ul>
|
|
<li>Bit 0 set indicates that the file is opened for
|
|
write-access.
|
|
<li>Bit 1 set indicates that the file has
|
|
been verified for consistency and is guaranteed to be
|
|
consistent with the format defined in this document.
|
|
<li>Bits 2-31 are reserved for future use.
|
|
</ul>
|
|
Bit 0 should be
|
|
set as the first action when a file is opened for write
|
|
access and should be cleared only as the final action
|
|
when closing a file. Bit 1 should be cleared during
|
|
normal access to a file and only set after the file's
|
|
consistency is guaranteed by the library or a
|
|
consistency utility.
|
|
</P>
|
|
|
|
<P><EM>This field is present in version 0+ of the superblock.</EM>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Indexed Storage Internal Node K</td>
|
|
<td>
|
|
<P>Each internal node of a indexed storage B-tree will have at
|
|
least this many entries but not more than twice this
|
|
many. If the group has only one internal
|
|
node then it might have fewer entries.
|
|
</P>
|
|
<P>This value must be greater than zero.
|
|
</P>
|
|
<P>See the <A href="#Btrees">description</A> of B-trees below.
|
|
</P>
|
|
|
|
<P><EM>This field is present in version 1+ of the superblock.</EM>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Base Address</td>
|
|
<td>
|
|
<P>This is the absolute file address of the first byte of
|
|
the HDF5 data within the file. The library currently
|
|
constrains this value to be the absolute file address
|
|
of the super block itself when creating new files;
|
|
future versions of the library may provide greater
|
|
flexibility. When opening an existing file and this address does
|
|
not match the offset of the superblock, the library assumes
|
|
that the entire contents of the HDF5 file have been adjusted in
|
|
the file and adjusts the base address and end of file address to
|
|
reflect their new positions in the file. Unless otherwise noted,
|
|
all other file addresses are relative to this base
|
|
address.
|
|
</P>
|
|
|
|
<P><EM>This field is present in version 0+ of the superblock.</EM>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Address of Global Free-space Index</td>
|
|
<td>
|
|
<P>Free-space management is not yet defined in the HDF5
|
|
file format and is not handled by the library.
|
|
Currently this field always contains the
|
|
<A href="#UndefinedAddress">undefined address</A>.
|
|
</P>
|
|
|
|
<P><EM>This field is present in version 0+ of the superblock.</EM>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>End of File Address</td>
|
|
<td>
|
|
<P>This is the absolute file address of the first byte past
|
|
the end of all HDF5 data. It is used to determine whether a
|
|
file has been accidently truncated and as an address where
|
|
file data allocation can occur if space from the free list is
|
|
not used.
|
|
</P>
|
|
|
|
<P><EM>This field is present in version 0+ of the superblock.</EM>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Driver Information Block Address</td>
|
|
<td>
|
|
<P>This is the relative file address of the file driver
|
|
information block which contains driver-specific
|
|
information needed to reopen the file. If there is no
|
|
driver information block then this entry should be the
|
|
<A href="#UndefinedAddress">undefined address</A>.
|
|
</P>
|
|
|
|
<P><EM>This field is present in version 0+ of the superblock.</EM>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Root Group Symbol Table Entry</td>
|
|
<td>
|
|
<P>This is the <A href="#SymbolTableEntry">symbol table entry</A>
|
|
of the root group, which serves as the entry point into
|
|
the group graph for the file.
|
|
</P>
|
|
|
|
<P><EM>This field is present in version 0+ of the superblock.</EM>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<H3><A name="DriverInfo">
|
|
Disk Format: Level 0B - File Driver Info</A></H3>
|
|
|
|
<p>The <em>file driver information block</em> is an optional region of the
|
|
file which contains information needed by the file driver in
|
|
order to reopen a file. The format of the file driver information
|
|
block is:
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Driver Information Block
|
|
</caption>
|
|
|
|
<tr>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Version</td>
|
|
<td colspan=3>Reserved (zero)</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Driver Information Size (4 bytes)</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>Driver Identification (8 bytes)<br><br></td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br><br>Driver Information (<em>n</em> bytes)<br><br><br></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Version</td>
|
|
<td>
|
|
<P>The version number of the driver information block. The
|
|
file format documented here is version zero.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Driver Information Size</td>
|
|
<td>
|
|
<P>The size in bytes of the Driver Information part of this
|
|
structure.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Driver Identification</td>
|
|
<td>
|
|
<P>This is an eight-byte ASCII string without null
|
|
termination which identifies the driver and version number
|
|
of the Driver Information block. The predefined drivers
|
|
supplied with the HDF5 library are identified by the
|
|
letters <code>NCSA</code> followed by the first four characters of
|
|
the driver name. If the Driver Information block is not
|
|
the original version then the last letter(s) of the
|
|
identification will be replaced by a version number in
|
|
ASCII.
|
|
</P>
|
|
<P>
|
|
For example, the various versions of the <em>family driver</em>
|
|
will be identified by <code>NCSAfami</code>, <code>NCSAfam0</code>,
|
|
<code>NCSAfam1</code>, etc.
|
|
(<code>NCSAfami</code> is simply <code>NCSAfamily</code> truncated
|
|
to eight characters. Subsequent identifiers will be created by
|
|
substituting sequential numerical values for the final character,
|
|
starting with zero.)
|
|
</P>
|
|
<P>
|
|
Identification for user-defined drivers
|
|
is arbitrary but should be unique and avoid the four character
|
|
prefix "NCSA".
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Driver Information</td>
|
|
<td>Driver information is stored in a format defined by the
|
|
file driver and encoded/decoded by the driver callbacks
|
|
invoked from the <code>H5FD_sb_encode</code> and
|
|
<code>H5FD_sb_decode</code> functions.</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<BR>
|
|
<HR>
|
|
|
|
<h2><a name="FileInfra">
|
|
Disk Format: Level 1 - File Infrastructure</a></h2>
|
|
<h3><a name="Btrees">Disk Format: Level 1A - B-link Trees and B-tree Nodes</a></h3>
|
|
|
|
<p>B-link trees allow flexible storage for objects which tend to grow
|
|
in ways that cause the object to be stored discontiguously. B-trees
|
|
are described in various algorithms books including "Introduction to
|
|
Algorithms" by Thomas H. Cormen, Charles E. Leiserson, and Ronald
|
|
L. Rivest. The B-link tree, in which the sibling nodes at a
|
|
particular level in the tree are stored in a doubly-linked list,
|
|
is described in the "Efficient Locking for Concurrent Operations
|
|
on B-trees" paper by Phillip Lehman and S. Bing Yao as published
|
|
in the <cite>ACM Transactions on Database Systems</cite>, Vol. 6,
|
|
No. 4, December 1981.
|
|
|
|
<p>The B-link trees implemented by the file format contain one more
|
|
key than the number of children. In other words, each child
|
|
pointer out of a B-tree node has a left key and a right key.
|
|
The pointers out of internal nodes point to sub-trees while
|
|
the pointers out of leaf nodes point to symbol nodes and
|
|
raw data chunks.
|
|
Aside from that difference, internal nodes and leaf nodes
|
|
are identical.
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
B-tree Nodes
|
|
</caption>
|
|
|
|
<tr>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
|
|
<tr>
|
|
<td colspan=4>Signature</td>
|
|
|
|
<tr>
|
|
<td>Node Type</td>
|
|
<td>Node Level</td>
|
|
<td colspan=2>Entries Used</td>
|
|
|
|
<tr>
|
|
<td colspan=4>Address of Left Sibling<sup>O</sup></td>
|
|
|
|
<tr>
|
|
<td colspan=4>Address of Right Sibling<sup>O</sup></td>
|
|
|
|
<tr>
|
|
<td colspan=4>Key 0 (variable size)</td>
|
|
|
|
<tr>
|
|
<td colspan=4>Address of Child 0<sup>O</sup></td>
|
|
|
|
<tr>
|
|
<td colspan=4>Key 1 (variable size)</td>
|
|
|
|
<tr>
|
|
<td colspan=4>Address of Child 1<sup>O</sup></td>
|
|
|
|
<tr>
|
|
<td colspan=4>...</td>
|
|
|
|
<tr>
|
|
<td colspan=4>Key 2<em>K</em> (variable size)</td>
|
|
|
|
<tr>
|
|
<td colspan=4>Address of Child 2<em>K</em><sup>O</sup></td>
|
|
|
|
<tr>
|
|
<td colspan=4>Key 2<em>K</em>+1 (variable size)</td>
|
|
</table>
|
|
|
|
<table class=note>
|
|
<tr><td>
|
|
(Items marked with an 'O' the above table are
|
|
<br>
|
|
of the size specified in "Size of Offsets.")
|
|
</td></tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Signature</td>
|
|
<td>
|
|
<P>The ASCII character string "<code>TREE</code>" is
|
|
used to indicate the
|
|
beginning of a B-link tree node. This gives file
|
|
consistency checking utilities a better chance of
|
|
reconstructing a damaged file.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Node Type</td>
|
|
<td>
|
|
<P>Each B-link tree points to a particular type of data.
|
|
This field indicates the type of data as well as
|
|
implying the maximum degree <em>K</em> of the tree and
|
|
the size of each Key field.
|
|
</P>
|
|
|
|
<table class=list>
|
|
<tr>
|
|
<th width="30%">Node Type</th>
|
|
<th align=left>Description</th>
|
|
</tr>
|
|
<tr>
|
|
<td align=center>0</td>
|
|
<td>This tree points to group nodes.</td>
|
|
</tr>
|
|
<tr>
|
|
<td align=center>1</td>
|
|
<td>This tree points to raw data chunk nodes.</td>
|
|
</tr>
|
|
</table>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Node Level</td>
|
|
<td>
|
|
<P>The node level indicates the level at which this node
|
|
appears in the tree (leaf nodes are at level zero). Not
|
|
only does the level indicate whether child pointers
|
|
point to sub-trees or to data, but it can also be used
|
|
to help file consistency checking utilities reconstruct
|
|
damanged trees.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Entries Used</td>
|
|
<td>
|
|
<P>This determines the number of children to which this
|
|
node points. All nodes of a particular type of tree
|
|
have the same maximum degree, but most nodes will point
|
|
to less than that number of children. The valid child
|
|
pointers and keys appear at the beginning of the node
|
|
and the unused pointers and keys appear at the end of
|
|
the node. The unused pointers and keys have undefined
|
|
values.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Address of Left Sibling</td>
|
|
<td>
|
|
<P>This is the relative file address of the left sibling of
|
|
the current node. If the current
|
|
node is the left-most node at this level then this field
|
|
is the <A href="#UndefinedAddress">undefined address</A>.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Address of Right Sibling</td>
|
|
<td>
|
|
<P>This is the relative file address of the right sibling of
|
|
the current node. If the current
|
|
node is the right-most node at this level then this
|
|
field is the <A href="#UndefinedAddress">undefined address</A>.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Keys and Child Pointers</td>
|
|
<td>
|
|
<P>Each tree has 2<em>K</em>+1 keys with 2<em>K</em>
|
|
child pointers interleaved between the keys. The number
|
|
of keys and child pointers actually containing valid
|
|
values is determined by the node's <em>Entries Used</em> field.
|
|
If that field is <em>N</em> then the B-link tree contains
|
|
<em>N</em> child pointers and <em>N</em>+1 keys.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Key</td>
|
|
<td>
|
|
<P>The format and size of the key values is determined by
|
|
the type of data to which this tree points. The keys are
|
|
ordered and are boundaries for the contents of the child
|
|
pointer; that is, the key values represented by child
|
|
<em>N</em> fall between Key <em>N</em> and Key
|
|
<em>N</em>+1. Whether the interval is open or closed on
|
|
each end is determined by the type of data to which the
|
|
tree points.
|
|
</P>
|
|
|
|
<P>
|
|
The format of the key depends on the node type.
|
|
For nodes of node type 0 (group nodes), the key is formatted as
|
|
follows:
|
|
<center>
|
|
<table class=list>
|
|
<tr>
|
|
<td width=30%>A single field of <i>Size of Lengths</i>
|
|
bytes:</td>
|
|
<td>Indicates the byte offset into the local heap
|
|
for the first object name in the subtree which
|
|
that key describes.
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
</P>
|
|
|
|
<P>
|
|
For nodes of node type 1 (chunked raw data nodes), the key is
|
|
formatted as follows:
|
|
<center>
|
|
<table class=list>
|
|
<tr>
|
|
<td width=30%>Bytes 1-4:</td>
|
|
<td>Size of chunk in bytes.</td>
|
|
</tr>
|
|
<tr>
|
|
<td>Bytes 4-8:</td>
|
|
<td>Filter mask, a 32-bit bitfield indicating which
|
|
filters have been skipped for this chunk. Each filter
|
|
has an index number in the pipeline (starting at 0, with
|
|
the first filter to apply) and if that filter is skipped,
|
|
the bit corresponding to it's index is set.</td>
|
|
</tr>
|
|
<tr>
|
|
<td><em>N</em> 64-bit fields:</td>
|
|
<td>A 64-bit index indicating the offset of the
|
|
chunk within the dataset where <i>N</i> is the number
|
|
of dimensions of the dataset. For example, if
|
|
a chunk in a 3-dimensional dataset begins at the
|
|
position <code>[5,5,5]</code>, there will be three
|
|
such 64-bit indices, each with the value of
|
|
<code>5</code>.</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Child Pointer</td>
|
|
<td>
|
|
<P>The tree node contains file addresses of subtrees or
|
|
data depending on the node level. Nodes at Level 0 point
|
|
to data addresses, either raw data chunk or group nodes.
|
|
Nodes at non-zero levels point to other nodes of the
|
|
same B-tree.
|
|
</P>
|
|
<P>For raw data chunk nodes, the child pointer is the address
|
|
of a single raw data chunk. For group nodes, the child pointer
|
|
points to a <A href="#SymbolTable">symbol table</A>, which contains
|
|
information for multiple symbol table entries.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<p>
|
|
Conceptually, each B-tree node looks like this:
|
|
<center>
|
|
<table>
|
|
<tr valign=top align=center>
|
|
<td>key[0]</td><td> </td>
|
|
<td>child[0]</td><td> </td>
|
|
<td>key[1]</td><td> </td>
|
|
<td>child[1]</td><td> </td>
|
|
<td>key[2]</td><td> </td>
|
|
<td>...</td><td> </td>
|
|
<td>...</td><td> </td>
|
|
<td>key[<i>N</i>-1]</td><td> </td>
|
|
<td>child[<i>N</i>-1]</td><td> </td>
|
|
<td>key[<i>N</i>]</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
<br>
|
|
|
|
where child[<i>i</i>] is a pointer to a sub-tree (at a level
|
|
above Level 0) or to data (at Level 0).
|
|
Each key[<i>i</i>] describes an <i>item</i> stored by the B-tree
|
|
(a chunk or an object of a group node). The range of values
|
|
represented by child[<i>i</i>] is indicated by key[<i>i</i>]
|
|
and key[<i>i</i>+1].
|
|
|
|
|
|
<p>The following question must next be answered:
|
|
"Is the value described by key[<i>i</i>] contained in
|
|
child[<i>i</i>-1] or in child[<i>i</i>]?"
|
|
The answer depends on the type of tree.
|
|
In trees for groups (node type 0) the object described by
|
|
key[<i>i</i>] is the greatest object contained in
|
|
child[<i>i</i>-1] while in chunk trees (node type 1) the
|
|
chunk described by key[<i>i</i>] is the least chunk in
|
|
child[<i>i</i>].
|
|
|
|
<p>That means that key[0] for group trees is sometimes unused;
|
|
it points to offset zero in the heap, which is always the
|
|
empty string and compares as "less-than" any valid object name.
|
|
|
|
<p>And key[<i>N</i>] for chunk trees is sometimes unused;
|
|
it contains a chunk offset which compares as "greater-than"
|
|
any other chunk offset and has a chunk byte size of zero
|
|
to indicate that it is not actually allocated.
|
|
|
|
|
|
<h3><a name="SymbolTable">Disk Format: Level 1B - Group and Symbol Nodes</a></h3>
|
|
|
|
<p>A group is an object internal to the file that allows
|
|
arbitrary nesting of objects within the file (including other groups).
|
|
A group maps a set of names in the group to a set of relative
|
|
file addresses where objects with those names are located in
|
|
the file. Certain metadata for an object to which the group points
|
|
can be cached in the group's symbol table in addition to the
|
|
object's header.
|
|
|
|
<p>An HDF5 object name space can be stored hierarchically by
|
|
partitioning the name into components and storing each
|
|
component in a group. The group entry for a
|
|
non-ultimate component points to the group containing
|
|
the next component. The group entry for the last
|
|
component points to the object being named.
|
|
|
|
<p>A group is a collection of group nodes pointed
|
|
to by a B-link tree. Each group node contains entries
|
|
for one or more symbols. If an attempt is made to add a
|
|
symbol to an already full group node containing
|
|
2<em>K</em> entries, then the node is split and one node
|
|
contains <em>K</em> symbols and the other contains
|
|
<em>K</em>+1 symbols.
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Group Node (A Leaf of a B-tree)
|
|
</caption>
|
|
|
|
<tr>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
|
|
<tr>
|
|
<td colspan=4>Signature</td>
|
|
|
|
<tr>
|
|
<td>Version Number</td>
|
|
<td>Reserved (0)</td>
|
|
<td colspan=2>Number of Symbols</td>
|
|
|
|
<tr>
|
|
<td colspan=4><br><br>Group Entries<br><br><br></td>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Signature</td>
|
|
<td>
|
|
<P>The ASCII character string "<code>SNOD</code>" is
|
|
used to indicate the
|
|
beginning of a group node. This gives file
|
|
consistency checking utilities a better chance of
|
|
reconstructing a damaged file.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Version Number</td>
|
|
<td>
|
|
<P>The version number for the group node. This
|
|
document describes version 1. (There is no version '0'
|
|
of the group node)
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Number of Symbols</td>
|
|
<td>
|
|
<P>Although all group nodes have the same length,
|
|
most contain fewer than the maximum possible number of
|
|
symbol entries. This field indicates how many entries
|
|
contain valid data. The valid entries are packed at the
|
|
beginning of the group node while the remaining
|
|
entries contain undefined values.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Group Entries</td>
|
|
<td>
|
|
<P>Each symbol has an entry in the group node.
|
|
The format of the entry is described below.
|
|
There are 2<EM>K</EM> entries in each group node, where
|
|
<EM>K</EM> is the "Group Leaf Node K" value from the
|
|
<A href="#SuperBlock">super block</A>.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<h3><a name="SymbolTableEntry">
|
|
Disk Format: Level 1C - Group Entry </a></h3>
|
|
|
|
<p>Each group entry in a group node is designed
|
|
to allow for very fast browsing of stored objects.
|
|
Toward that design goal, the group entries
|
|
include space for caching certain constant metadata from the
|
|
object header.
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Group Entry
|
|
</caption>
|
|
|
|
<tr>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Name Offset<sup>O</sup></td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Object Header Address<sup>O</sup></td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Cache Type</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Reserved</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br><br>Scratch-pad Space (16 bytes)<br><br><br></td>
|
|
</tr>
|
|
</table>
|
|
|
|
<table class=note>
|
|
<tr><td>
|
|
(Items marked with an 'O' the above table are
|
|
<br>
|
|
of the size specified in "Size of Offsets.")
|
|
</td></tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Name Offset</td>
|
|
<td>
|
|
<P>This is the byte offset into the group local
|
|
heap for the name of the object. The name is null
|
|
terminated.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Object Header Address</td>
|
|
<td>
|
|
<P>Every object has an object header which serves as a
|
|
permanent location for the object's metadata. In addition
|
|
to appearing in the object header, some metadata can be
|
|
cached in the scratch-pad space.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Cache Type</td>
|
|
<td>
|
|
<P>The cache type is determined from the object header.
|
|
It also determines the format for the scratch-pad space:
|
|
<br>
|
|
<table class=list>
|
|
<tr align=left>
|
|
<th>Type:</th>
|
|
<th>Description:</th>
|
|
</tr>
|
|
<tr>
|
|
<td width="10%" align=center>0</td>
|
|
<td>No data is cached by the group entry. This
|
|
is guaranteed to be the case when an object header
|
|
has a link count greater than one.
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td align=center>1</td>
|
|
<td>Object header metadata is cached in the group
|
|
entry. This implies that the group
|
|
entry refers to another group.
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td align=center>2</td>
|
|
<td>The entry is a symbolic link. The first four bytes
|
|
of the scratch-pad space are the offset into the local
|
|
heap for the link value. The object header address
|
|
will be undefined.
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td align=center><em>N</em></td>
|
|
<td>Other cache values can be defined later and
|
|
libraries that do not understand the new values will
|
|
still work properly.
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Reserved</td>
|
|
<td>
|
|
<P>These four bytes are present so that the scratch-pad
|
|
space is aligned on an eight-byte boundary. They are
|
|
always set to zero.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Scratch-pad Space</td>
|
|
<td>
|
|
<P>This space is used for different purposes, depending
|
|
on the value of the Cache Type field. Any metadata
|
|
about a dataset object represented in the scratch-pad
|
|
space is duplicated in the object header for that
|
|
dataset. This metadata can include the datatype
|
|
and the size of the dataspace for a dataset whose datatype
|
|
is atomic and whose dataspace is fixed and less than
|
|
four dimensions.
|
|
</P>
|
|
<P>
|
|
Furthermore, no data is cached in the group
|
|
entry scratch-pad space if the object header for
|
|
the group entry has a link count greater than
|
|
one.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<h4>Format of the Scratch-pad Space</h4>
|
|
|
|
<p>The group entry scratch-pad space is formatted
|
|
according to the value in the Cache Type field.
|
|
|
|
<p>If the Cache Type field contains the value zero
|
|
<code>(0)</code> then no information is
|
|
stored in the scratch-pad space.
|
|
|
|
<p>If the Cache Type field contains the value one
|
|
<code>(1)</code>, then the scratch-pad space
|
|
contains cached metadata for another object header
|
|
in the following format:
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Object Header Scratch-pad Format
|
|
</caption>
|
|
|
|
<tr>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
|
|
<tr>
|
|
<td colspan=4>Address of B-tree<sup>O</sup></td>
|
|
|
|
<tr>
|
|
<td colspan=4>Address of Name Heap<sup>O</sup></td>
|
|
</table>
|
|
|
|
<table class=note>
|
|
<tr><td>
|
|
(Items marked with an 'O' the above table are
|
|
<br>
|
|
of the size specified in "Size of Offsets.")
|
|
</td></tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Address of B-tree</td>
|
|
<td>
|
|
<P>This is the file address for the root of the
|
|
group's B-tree.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Address of Name Heap</td>
|
|
<td>
|
|
<P>This is the file address for the group's local
|
|
heap, in which are stored the group's symbol names.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
|
|
<P>If the Cache Type field contains the value two
|
|
<code>(2)</code>, then the scratch-pad space
|
|
contains cached metadata for another symbolic link
|
|
in the following format:
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Symbolic Link Scratch-pad Format
|
|
</caption>
|
|
|
|
<tr>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Offset to Link Value</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Offset to Link Value</td>
|
|
<td>
|
|
<P>The value of a symbolic link (that is, the name of the
|
|
thing to which it points) is stored in the local heap.
|
|
This field is the 4-byte offset into the local heap for
|
|
the start of the link value, which is null terminated.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<h3><a name="LocalHeap">Disk Format: Level 1D - Local Heaps</a></h3>
|
|
|
|
<P>A heap is a collection of small heap objects. Objects can be
|
|
inserted and removed from the heap at any time.
|
|
The address of a heap does not change once the heap is created.
|
|
References to objects are stored in the group table;
|
|
the names of those objects are stored in the local heap.
|
|
</P>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Local Heap
|
|
</caption>
|
|
|
|
<tr>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Signature</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Version</td>
|
|
<td colspan=3>Reserved (zero)</td>
|
|
</td>
|
|
|
|
<tr>
|
|
<td colspan=4>Data Segment Size<sup>L</sup></td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Offset to Head of Free-list<sup>L</sup></td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Address of Data Segment<sup>O</sup></td>
|
|
</tr>
|
|
</table>
|
|
|
|
<table class=note>
|
|
<tr><td>
|
|
(Items marked with an 'L' the above table are
|
|
<br>
|
|
of the size specified in "Size of Lengths.")
|
|
</td></tr>
|
|
<tr><td>
|
|
(Items marked with an 'O' the above table are
|
|
<br>
|
|
of the size specified in "Size of Offsets.")
|
|
</td></tr>
|
|
</table>
|
|
</div>
|
|
|
|
<p>
|
|
<center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Signature</td>
|
|
<td>
|
|
<P>The ASCII character string "<code>HEAP</code>"
|
|
is used to indicate the
|
|
beginning of a heap. This gives file consistency
|
|
checking utilities a better chance of reconstructing a
|
|
damaged file.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Version</td>
|
|
<td>
|
|
<P>Each local heap has its own version number so that new
|
|
heaps can be added to old files. This document
|
|
describes version zero (0) of the local heap.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Data Segment Size</td>
|
|
<td>
|
|
<P>The total amount of disk memory allocated for the heap
|
|
data. This may be larger than the amount of space
|
|
required by the objects stored in the heap. The extra
|
|
unused space in the heap holds a linked list of free blocks.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Offset to Head of Free-list</td>
|
|
<td>
|
|
<P>This is the offset within the heap data segment of the
|
|
first free block (or the
|
|
<A href="#UndefinedAddress">undefined address</A> if there is no
|
|
free block). The free block contains "Size of Lengths" bytes that
|
|
are the offset of the next free block (or the
|
|
value '1' if this is the
|
|
last free block) followed by "Size of Lengths" bytes that store
|
|
the size of this free block. The size of the free block includes
|
|
the space used to store the offset of the next free block and
|
|
the of the current block, making the minimum size of a free block
|
|
2 * "Size of Lengths".
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Address of Data Segment</td>
|
|
<td>
|
|
<P>The data segment originally starts immediately after
|
|
the heap header, but if the data segment must grow as a
|
|
result of adding more objects, then the data segment may
|
|
be relocated, in its entirety, to another part of the
|
|
file.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<p>Objects within the heap should be aligned on an 8-byte boundary.
|
|
|
|
<h3><a name="GlobalHeap">Disk Format: Level 1E - Global Heap</a></h3>
|
|
|
|
<P>Each HDF5 file has a global heap which stores various types of
|
|
information which is typically shared between datasets. The
|
|
global heap was designed to satisfy these goals:
|
|
|
|
<ol type="A">
|
|
<li>Repeated access to a heap object must be efficient without
|
|
resulting in repeated file I/O requests. Since global heap
|
|
objects will typically be shared among several datasets, it is
|
|
probable that the object will be accessed repeatedly.
|
|
<li>Collections of related global heap objects should result in
|
|
fewer and larger I/O requests. For instance, a dataset of
|
|
object references will have a global heap object for each
|
|
reference. Reading the entire set of object references
|
|
should result in a few large I/O requests instead of one small
|
|
I/O request for each reference.
|
|
<li>It should be possible to remove objects from the global heap
|
|
and the resulting file hole should be eligible to be reclaimed
|
|
for other uses.
|
|
</ol>
|
|
</P>
|
|
|
|
<P>The implementation of the heap makes use of the memory
|
|
management already available at the file level and combines that
|
|
with a new top-level object called a <em>collection</em> to
|
|
achieve Goal B. The global heap is the set of all collections.
|
|
Each global heap object belongs to exactly one collection and
|
|
each collection contains one or more global heap objects. For
|
|
the purposes of disk I/O and caching, a collection is treated as
|
|
an atomic object.
|
|
</P>
|
|
|
|
<P>The HDF5 library creates global heap collections as needed, so there may
|
|
be multiple collections throughout the file. The set of all of them is
|
|
abstractly called the "global heap", although they don't actually link
|
|
to each other, and there is no global place in the file where you can
|
|
discover all of the collections. The collections are found simply by
|
|
finding a reference to one through another object in the file (eg.
|
|
variable-length datatype elements, etc).
|
|
</P>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
A Global Heap Collection
|
|
</caption>
|
|
|
|
<tr>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Signature</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Version</td>
|
|
<td colspan=3>Reserved (zero)</td>
|
|
</td>
|
|
|
|
<tr>
|
|
<td colspan=4>Collection Size<sup>L</sup></td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>Global Heap Object 1<br><br></td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>Global Heap Object 2<br><br></td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>...<br><br></td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>Global Heap Object <em>N</em><br><br></td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>Global Heap Object 0 (free space)<br><br></td>
|
|
</tr>
|
|
</table>
|
|
|
|
<table class=note>
|
|
<tr><td>
|
|
(Items marked with an 'L' the above table are
|
|
<br>
|
|
of the size specified in "Size of Lengths.")
|
|
</td></tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Signature</td>
|
|
<td>
|
|
<P>The ASCII character string "<code>GCOL</code>"
|
|
is used to indicate the
|
|
beginning of a collection. This gives file consistency
|
|
checking utilities a better chance of reconstructing a
|
|
damaged file.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Version</td>
|
|
<td>
|
|
<P>Each collection has its own version number so that new
|
|
collections can be added to old files. This document
|
|
describes version one (1) of the collections (there is no
|
|
version zero (0)).
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Collection Size</td>
|
|
<td>
|
|
<P>This is the size in bytes of the entire collection
|
|
including this field. The default (and minimum)
|
|
collection size is 4096 bytes which is a typical file
|
|
system block size. This allows for 127 16-byte heap
|
|
objects plus their overhead (the collection header of 16 bytes
|
|
and the 16 bytes of information about each heap object).
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Global Heap Object 1 through <em>N</em></td>
|
|
<td>
|
|
<P>The objects are stored in any order with no
|
|
intervening unused space.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Global Heap Object 0</td>
|
|
<td>
|
|
<P>Global Heap Object 0 (zero), when present, represents the free
|
|
space in the collection. Free space always appears at the end of
|
|
the collection. If the free space is too small to store the header
|
|
for Object 0 (described below) then the header is implied and the
|
|
collection contains no free space.
|
|
</P>
|
|
</td>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Global Heap Object
|
|
</caption>
|
|
|
|
<tr>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=2>Heap Object ID</td>
|
|
<td colspan=2>Reference Count</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Reserved</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Object Size<sup>L</sup></td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>Object Data<br><br></td>
|
|
</tr>
|
|
</table>
|
|
|
|
<table class=note>
|
|
<tr><td>
|
|
(Items marked with an 'L' the above table are
|
|
<br>
|
|
of the size specified in "Size of Lengths.")
|
|
</td></tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Heap Object ID</td>
|
|
<td>
|
|
<P>Each object has a unique identification number within a
|
|
collection. The identification numbers are chosen so that
|
|
new objects have the smallest value possible with the
|
|
exception that the identifier <code>0</code> always refers to the
|
|
object which represents all free space within the
|
|
collection.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Reference Count</td>
|
|
<td>
|
|
<P>All heap objects have a reference count field. An
|
|
object which is referenced from some other part of the
|
|
file will have a positive reference count. The reference
|
|
count for Object 0 is always zero.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Reserved</td>
|
|
<td>
|
|
<P>Zero padding to align next field on an 8-byte boundary.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Object Size</td>
|
|
<td>
|
|
<P>This is the size of the object data stored for the object.
|
|
The actual storage space allocated for the object data is rounded
|
|
up to a multiple of eight.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Object Data</td>
|
|
<td>
|
|
<P>The object data is treated as a one-dimensional array
|
|
of bytes to be interpreted by the caller.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<h3><a name="FreeSpaceIndex">Disk Format: Level 1F - Free-space Index</a></h3>
|
|
|
|
<p>The free-space index is a collection of blocks of data,
|
|
dispersed throughout the file, which are currently not used by
|
|
any file objects.
|
|
|
|
<p>The super block contains a pointer to root of the free-space description;
|
|
that pointer is currently required to be the
|
|
<A href="#UndefinedAddress">undefined address</A>.
|
|
|
|
<p>The format of the free-space index is not defined at this time.
|
|
|
|
<!--
|
|
<p>The Free-space Index is a collection of blocks of data,
|
|
dispersed throughout the file, which are currently not used by
|
|
any file objects. The blocks of data are indexed by a B-tree of
|
|
their length within the file.
|
|
|
|
|
|
<p>Each B-tree page is composed of the following entries and
|
|
B-tree management information, organized as follows:
|
|
|
|
<p>
|
|
<center>
|
|
<table border cellpadding=4 width="80%">
|
|
<caption align=bottom>
|
|
<B>HDF5 Free-space Heap Page</B>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Signature</td>
|
|
<tr align=center>
|
|
<td colspan=4>B-tree Left-link Offset</td>
|
|
<tr align=center>
|
|
<td colspan=4><br>Length of Free-block #1<br> <br></td>
|
|
<tr align=center>
|
|
<td colspan=4><br>Offset of Free-block #1<br> <br></td>
|
|
<tr align=center>
|
|
<td colspan=4>.<br>.<br>.<br></td>
|
|
<tr align=center>
|
|
<td colspan=4><br>Length of Free-block #n<br> <br></td>
|
|
<tr align=center>
|
|
<td colspan=4><br>Offset of Free-block #n<br> <br></td>
|
|
<tr align=center>
|
|
<td colspan=4>"High" Offset</td>
|
|
<tr align=center>
|
|
<td colspan=4>Right-link Offset</td>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<dl>
|
|
<dt> The elements of the free-space heap page are described below:
|
|
<dd>
|
|
<dl>
|
|
<dt>Signature: (4 bytes)
|
|
<dd>The ASCII character string <code>FREE</code>
|
|
is used to indicate the
|
|
beginning of a free-space heap B-tree page. This gives
|
|
file consistency checking utilities a better chance of
|
|
reconstructing a damaged file.
|
|
|
|
<dt>B-tree Left-link Offset: (<offset> bytes)
|
|
<dd>This value is used to indicate the offset of all offsets
|
|
in the B-link-tree which are smaller than the value of the
|
|
offset in entry #1. This value is also used to indicate a
|
|
leaf node in the B-link-tree by being set to all ones.
|
|
|
|
<dt>Length of Free-block #n: (<length> bytes)
|
|
<dd>This value indicates the length of an unused block in
|
|
the file.
|
|
|
|
<dt>Offset of Free-block #n: (<offset> bytes)
|
|
<dd>This value indicates the offset in the file of an
|
|
unused block in the file.
|
|
|
|
<dt>"High" Offset: (4-bytes)
|
|
<dd>This offset is used as the upper bound on offsets
|
|
contained within a page when the page has been split.
|
|
|
|
<dt>Right-link Offset: (<offset> bytes)
|
|
<dd>This value is used to indicate the offset of the next
|
|
child to the right of the parent of this group
|
|
page. When there is no node to the right, this value is
|
|
all zeros.
|
|
</dl>
|
|
</dl>
|
|
|
|
<p>The algorithms for searching and inserting objects in the
|
|
B-tree pages are described fully in the Lehman and Yao paper,
|
|
which should be read to provide a full description of the
|
|
B-tree's usage.
|
|
-->
|
|
|
|
<BR>
|
|
<HR>
|
|
|
|
<h2><a name="DataObject">Disk Format: Level 2 - Data Objects </a></h2>
|
|
|
|
<P>Data objects contain the real information in the file. These
|
|
objects compose the scientific data and other information which
|
|
are generally thought of as "data" by the end-user. All the
|
|
other information in the file is provided as a framework for
|
|
these data objects.
|
|
</P>
|
|
|
|
<P>A data object is composed of header information and data
|
|
information. The header information contains the information
|
|
needed to interpret the data information for the data object as
|
|
well as additional "metadata" or pointers to additional
|
|
"metadata" used to describe or annotate each data object.
|
|
</P>
|
|
|
|
<h3><a name="ObjectHeader">
|
|
Disk Format: Level 2A - Data Object Headers</a></h3>
|
|
|
|
<P>The header information of an object is designed to encompass
|
|
all the information about an object, except for the data itself.
|
|
This information includes
|
|
the dataspace, datatype, information about how the data
|
|
is stored on disk (in external files, compressed, broken up in
|
|
blocks, etc.), as well as other information used by the library
|
|
to speed up access to the data objects or maintain a file's
|
|
integrity. Information stored by user applications as attributes
|
|
is also stored in the object's header. The header of each object is
|
|
not necessarily located immediately prior to the object's data in the
|
|
file and in fact may be located in any position in the file. The order
|
|
of the messages in an object header is not significant.
|
|
</P>
|
|
|
|
<P>Header messages are aligned on 8-byte boundaries.
|
|
</P>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Object Headers
|
|
</caption>
|
|
|
|
<tr>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Version</td>
|
|
<td>Reserved (zero)</td>
|
|
<td colspan=2>Number of Header Messages</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Object Reference Count</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Object Header Size</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=2>Header Message Type #1</td>
|
|
<td colspan=2>Size of Header Message Data #1</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Header Message #1 Flags</td>
|
|
<td colspan=3>Reserved (zero)</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>Header Message Data #1<br><br></td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>.<br>.<br>.<br></td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=2>Header Message Type #n</td>
|
|
<td colspan=2>Size of Header Message Data #n</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Header Message #n Flags</td>
|
|
<td colspan=3>Reserved (zero)</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>Header Message Data #n<br><br></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Version</td>
|
|
<td>
|
|
<P>This value is used to determine the format of the
|
|
information in the object header. When the format of the
|
|
information in the object header is changed, the version number
|
|
is incremented and can be used to determine how the
|
|
information in the object header is formatted. This
|
|
document describes version one (1) (there was no version
|
|
zero (0)).
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Number of Header Messages</td>
|
|
<td>
|
|
<P>This value determines the number of messages listed in
|
|
object headers for this object. This value includes the messages
|
|
in continuation messages for this object.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Object Reference Count</td>
|
|
<td>
|
|
<P>This value specifies the number of "hard links" to this object
|
|
within the current file. References to the object from external
|
|
files, "soft links" in this file and object references in this
|
|
file are not tracked.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Object Header Size</td>
|
|
<td>
|
|
<P>This value specifies the number of bytes of header message data
|
|
following this length field that contain object header messages
|
|
for this object header. This value does not include the size of
|
|
object header continuation blocks for this object elsewhere in the
|
|
file.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Header Message Type</td>
|
|
<td>
|
|
<P>This value specifies the type of information included in the
|
|
following header message data. The header message types for the
|
|
pre-defined header messages are included in sections below.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Size of Header Message Data</td>
|
|
<td>
|
|
<P>This value specifies the number of bytes of header
|
|
message data following the header message type and length
|
|
information for the current message. The size includes
|
|
padding bytes to make the message a multiple of eight
|
|
bytes.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Header Message Flags</td>
|
|
<td>
|
|
<P>This is a bit field with the following definition:
|
|
<table class=list>
|
|
<tr>
|
|
<th width="30%">Bit</th>
|
|
<th align=left>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>0</code></td>
|
|
<td>If set, the message data is constant. This is used
|
|
for messages like the datatype message of a dataset.
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td align=center><code>1</code></td>
|
|
<td>If set, the message is stored in the global heap.
|
|
The Header Message Data field contains a Shared Object
|
|
message and the Size of Header Message Data field
|
|
contains the size of that Shared Object message.
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td align=center><code>2-7</code></td>
|
|
<td>Reserved</td>
|
|
</tr>
|
|
</table>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Header Message Data</td>
|
|
<td>
|
|
<P>The format and length of this field is determined by the
|
|
header message type and size respectively. Some header
|
|
message types do not require any data and this information
|
|
can be eliminated by setting the length of the message to
|
|
zero. The data is padded with enough zeros to make the
|
|
size a multiple of eight.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<P>The header message types and the message data associated with
|
|
them compose the critical "metadata" about each object. Some
|
|
header messages are required for each object while others are
|
|
optional. Some optional header messages may also be repeated
|
|
several times in the header itself, the requirements and number
|
|
of times allowed in the header will be noted in each header
|
|
message description below.
|
|
</P>
|
|
|
|
<P>The following is a list of currently defined header messages:
|
|
</P>
|
|
|
|
<hr>
|
|
<h4><a name="NILMessage">Name: NIL</a></h4>
|
|
|
|
<P class=item><B>Header Message Type: </B>0x0000
|
|
</P>
|
|
<P class=item><B>Length:</B> varies
|
|
</P>
|
|
<P class=item><B>Status:</B> Optional, may be repeated.
|
|
</P>
|
|
<P class=item><B>Purpose and Description:</B> The NIL message is used to indicate a
|
|
message which is to be ignored when reading the header messages for a
|
|
data object. [Possibly one which has been deleted for some reason.]
|
|
</P>
|
|
<P class=item><B>Format of Data:</B> Unspecified.
|
|
</P>
|
|
|
|
<hr>
|
|
<h4><a name="SimpleDataSpace">Name: Simple Dataspace</a></h4>
|
|
|
|
<P class=item><B>Header Message Type: </B>0x0001
|
|
</P>
|
|
<P class=item><B>Length:</B> Varies according to the number of dimensions,
|
|
as described in the following table.
|
|
</P>
|
|
<P class=item><B>Status:</B> Required for dataset objects, may not be
|
|
repeated.
|
|
</P>
|
|
<P class=item><B>Description:</B> The simple dataspace message describes the
|
|
number of dimensions (i.e. "rank") and size of each dimension that the
|
|
data object has. This message is only used for datasets which have a
|
|
simple, rectilinear grid layout; datasets requiring a more complex
|
|
layout (irregularly structured or unstructured grids, etc.) must use
|
|
the <em>Complex Dataspace</em> message for expressing the space the
|
|
dataset inhabits. <i>(Note: The <em>Complex Dataspace</em>
|
|
functionality is not yet implemented and it is not described in this
|
|
document.)</i>
|
|
</P>
|
|
|
|
<P class=item><B>Format of Data:</B>
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Simple Dataspace Message
|
|
</caption>
|
|
|
|
<tr>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
<th>byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Version</td>
|
|
<td>Dimensionality</td>
|
|
<td>Flags</td>
|
|
<td>Reserved</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Reserved</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Dimension #1 Size<sup>L</sup></td>
|
|
<tr>
|
|
<td colspan=4>.<br>.<br>.<br></td>
|
|
<tr>
|
|
<td colspan=4>Dimension #n Size<sup>L</sup></td>
|
|
<tr>
|
|
<td colspan=4>Dimension #1 Maximum Size<sup>L</sup></td>
|
|
<tr>
|
|
<td colspan=4>.<br>.<br>.<br></td>
|
|
<tr>
|
|
<td colspan=4>Dimension #n Maximum Size<sup>L</sup></td>
|
|
<tr>
|
|
<td colspan=4>Permutation Index #1<sup>L</sup></td>
|
|
<tr>
|
|
<td colspan=4>.<br>.<br>.<br></td>
|
|
<tr>
|
|
<td colspan=4>Permutation Index #n<sup>L</sup></td>
|
|
</table>
|
|
|
|
<table class=note>
|
|
<tr><td>
|
|
(Items marked with an 'L' the above table are
|
|
<br>
|
|
of the size specified in "Size of Lengths.")
|
|
</td></tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Version</td>
|
|
<td>
|
|
<P>This value is used to determine the format of the
|
|
Simple Dataspace Message. When the format of the
|
|
information in the message is changed, the version number
|
|
is incremented and can be used to determine how the
|
|
information in the object header is formatted. This
|
|
document describes version one (1) (there was no version
|
|
zero (0)).
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Dimensionality</td>
|
|
<td>
|
|
<P>This value is the number of dimensions that the data
|
|
object has.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Flags</td>
|
|
<td>
|
|
<P>This field is used to store flags to indicate the
|
|
presence of parts of this message. Bit 0 (the least
|
|
significant bit) is used to indicate that maximum
|
|
dimensions are present. Bit 1 is used to indicate that
|
|
permutation indices are present.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Dimension #n Size</td>
|
|
<td>
|
|
<P>This value is the current size of the dimension of the
|
|
data as stored in the file. The first dimension stored in
|
|
the list of dimensions is the slowest changing dimension
|
|
and the last dimension stored is the fastest changing
|
|
dimension.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Dimension #n Maximum Size</td>
|
|
<td>
|
|
<P>This value is the maximum size of the dimension of the
|
|
data as stored in the file. This value may be the special
|
|
"<A href="#UnlimitedDim">unlimited</A>" size which indicates
|
|
that the data may expand along this dimension indefinitely.
|
|
If these values are not stored, the maximum size of each
|
|
dimension is assumed to be the dimension's current size.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Permutation Index #n</td>
|
|
<td>
|
|
<P>This value is the index permutation used to map
|
|
each dimension from the canonical representation to an
|
|
alternate axis for each dimension. If these values are
|
|
not stored, the first dimension stored in the list of
|
|
dimensions is the slowest changing dimension and the last
|
|
dimension stored is the fastest changing dimension.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
</P>
|
|
|
|
<!--
|
|
<hr>
|
|
<h4><a name="DataSpaceMessage">Name: Complex Dataspace (Fiber Bundle?)</a></h4>
|
|
<b>Header Message Type: </b>0x0002<br>
|
|
<b>Length:</b> varies<br>
|
|
|
|
<b>Status:</b> One of the <em>Simple Dataspace</em> or
|
|
<em>Complex Dataspace</em> messages is required (but not both) and may
|
|
not be repeated.<br> <b>Purpose and Description:</b> The
|
|
<em>Dataspace</em> message describes space that the dataset is
|
|
mapped onto in a more comprehensive way than the <em>Simple
|
|
Dimensionality</em> message is capable of handling. The
|
|
dataspace of a dataset encompasses the type of coordinate system
|
|
used to locate the dataset's elements as well as the structure and
|
|
regularity of the coordinate system. The dataspace also
|
|
describes the number of dimensions which the dataset inhabits as
|
|
well as a possible higher dimensional space in which the dataset
|
|
is located within.
|
|
|
|
<br>
|
|
<b>Format of Data:</b>
|
|
|
|
<center>
|
|
<table border cellpadding=4 width="80%">
|
|
<caption align=bottom>
|
|
<B>HDF5 Dataspace Message Layout</B>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Mesh Type</td>
|
|
<tr align=center>
|
|
<td colspan=4>Logical Dimensionality</td>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<dl>
|
|
<dt>The elements of the dimensionality message are described below:
|
|
<dd>
|
|
<dl>
|
|
<dt>Mesh Type: (unsigned 32-bit integer)
|
|
<dd>This value indicates whether the grid is
|
|
polar/spherical/cartesion,
|
|
structured/unstructured and regular/irregular. <br>
|
|
The mesh type value is broken up as follows: <br>
|
|
|
|
<P>
|
|
<center>
|
|
<table border cellpadding=4 width="80%">
|
|
<caption align=bottom>
|
|
<B>HDF5 Mesh-type Layout</B>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
|
|
<tr align=center>
|
|
<td colspan=1>Mesh Embedding</td>
|
|
<td colspan=1>Coordinate System</td>
|
|
<td colspan=1>Structure</td>
|
|
<td colspan=1>Regularity</td>
|
|
</table>
|
|
</center>
|
|
The following are the definitions of mesh-type bytes:
|
|
<dl>
|
|
<dt>Mesh Embedding
|
|
<dd>This value indicates whether the dataset dataspace
|
|
is located within
|
|
another dataspace or not:
|
|
<dl> <dl>
|
|
<dt><STANDALONE>
|
|
<dd>The dataset mesh is self-contained and is not
|
|
embedded in another mesh.
|
|
<dt><EMBEDDED>
|
|
<dd>The dataset's dataspace is located within
|
|
another dataspace, as
|
|
described in information below.
|
|
</dl> </dl>
|
|
<dt>Coordinate System
|
|
<dd>This value defines the type of coordinate system
|
|
used for the mesh:
|
|
<dl> <dl>
|
|
<dt><POLAR>
|
|
<dd>The last two dimensions are in polar
|
|
coordinates, higher dimensions are
|
|
cartesian.
|
|
<dt><SPHERICAL>
|
|
<dd>The last three dimensions are in spherical
|
|
coordinates, higher dimensions
|
|
are cartesian.
|
|
<dt><CARTESIAN>
|
|
<dd>All dimensions are in cartesian coordinates.
|
|
</dl> </dl>
|
|
<dt>Structure
|
|
<dd>This value defines the locations of the grid-points
|
|
on the axes:
|
|
<dl> <dl>
|
|
<dt><STRUCTURED>
|
|
<dd>All grid-points are on integral, sequential
|
|
locations, starting from 0.
|
|
<dt><UNSTRUCTURED>
|
|
<dd>Grid-points locations in each dimension are
|
|
explicitly defined and
|
|
may be of any numeric datatype.
|
|
</dl> </dl>
|
|
<dt>Regularity
|
|
<dd>This value defines the locations of the dataset
|
|
points on the grid:
|
|
<dl> <dl>
|
|
<dt><REGULAR>
|
|
<dd>All dataset elements are located at the
|
|
grid-points defined.
|
|
<dt><IRREGULAR>
|
|
<dd>Each dataset element has a particular
|
|
grid-location defined.
|
|
</dl> </dl>
|
|
</dl>
|
|
<p>The following grid combinations are currently allowed:
|
|
<dl> <dl>
|
|
<dt><POLAR-STRUCTURED-REGULAR>
|
|
<dt><SPHERICAL-STRUCTURED-REGULAR>
|
|
<dt><CARTESIAN-STRUCTURED-REGULAR>
|
|
<dt><POLAR-UNSTRUCTURED-REGULAR>
|
|
<dt><SPHERICAL-UNSTRUCTURED-REGULAR>
|
|
<dt><CARTESIAN-UNSTRUCTURED-REGULAR>
|
|
<dt><CARTESIAN-UNSTRUCTURED-IRREGULAR>
|
|
</dl> </dl>
|
|
All of the above grid types can be embedded within another
|
|
dataspace.
|
|
<br> <br>
|
|
<dt>Logical Dimensionality: (unsigned 32-bit integer)
|
|
<dd>This value is the number of dimensions that the dataset occupies.
|
|
|
|
<P>
|
|
<center>
|
|
<table border cellpadding=4 width="80%">
|
|
<caption align=bottom>
|
|
<B>HDF5 Dataspace Embedded Dimensionality Information</B>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Embedded Dimensionality</td>
|
|
<tr align=center>
|
|
<td colspan=4>Embedded Dimension Size #1</td>
|
|
<tr align=center>
|
|
<td colspan=4>.<br>.<br>.<br></td>
|
|
<tr align=center>
|
|
<td colspan=4>Embedded Dimension Size #n</td>
|
|
<tr align=center>
|
|
<td colspan=4>Embedded Origin Location #1</td>
|
|
<tr align=center>
|
|
<td colspan=4>.<br>.<br>.<br></td>
|
|
<tr align=center>
|
|
<td colspan=4>Embedded Origin Location #n</td>
|
|
</table>
|
|
</center>
|
|
|
|
<dt>Embedded Dimensionality: (unsigned 32-bit integer)
|
|
<dd>This value is the number of dimensions of the space the
|
|
dataset is located
|
|
within. i.e. a planar dataset located within a 3-D space,
|
|
or a 3-D dataset
|
|
which is a subset of another 3-D space, etc.
|
|
<dt>Embedded Dimension Size: (unsigned 32-bit integer)
|
|
<dd>These values are the sizes of the dimensions of the
|
|
embedded dataspace
|
|
that the dataset is located within.
|
|
<dt>Embedded Origin Location: (unsigned 32-bit integer)
|
|
<dd>These values comprise the location of the dataset's
|
|
origin within the embedded dataspace.
|
|
</dl>
|
|
</dl>
|
|
[Comment: need some way to handle different orientations of the
|
|
dataset dataspace
|
|
within the embedded dataspace]<br>
|
|
|
|
<P>
|
|
<center>
|
|
<table border cellpadding=4 width="80%">
|
|
<caption align=bottom>
|
|
<B>HDF5 Dataspace Structured/Regular Grid Information</B>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Logical Dimension Size #1</td>
|
|
<tr align=center>
|
|
<td colspan=4>Logical Dimension Maximum #1</td>
|
|
<tr align=center>
|
|
<td colspan=4>.<br>.<br>.<br></td>
|
|
<tr align=center>
|
|
<td colspan=4>Logical Dimension Size #n</td>
|
|
<tr align=center>
|
|
<td colspan=4>Logical Dimension Maximum #n</td>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<dl>
|
|
<dt>The elements of the dimensionality message are described below:
|
|
<dd>
|
|
<dl>
|
|
<dt>Logical Dimension Size #n: (unsigned 32-bit integer)
|
|
<dd>This value is the current size of the dimension of the
|
|
data as stored in
|
|
the file. The first dimension stored in the list of
|
|
dimensions is the slowest
|
|
changing dimension and the last dimension stored is the
|
|
fastest changing
|
|
dimension.
|
|
<dt>Logical Dimension Maximum #n: (unsigned 32-bit integer)
|
|
<dd>This value is the maximum size of the dimension of the
|
|
data as stored in
|
|
the file. This value may be the special value
|
|
<UNLIMITED> which
|
|
indicates that the data may expand along this dimension
|
|
indefinitely.
|
|
</dl>
|
|
</dl>
|
|
<P>
|
|
<center>
|
|
<table border cellpadding=4 width="80%">
|
|
<caption align=bottom>
|
|
<B>HDF5 Dataspace Structured/Irregular Grid Information</B>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
|
|
<tr align=center>
|
|
<td colspan=4># of Grid Points in Dimension #1</td>
|
|
<tr align=center>
|
|
<td colspan=4>.<br>.<br>.<br></td>
|
|
<tr align=center>
|
|
<td colspan=4># of Grid Points in Dimension #n</td>
|
|
<tr align=center>
|
|
<td colspan=4>Datatype of Grid Point Locations</td>
|
|
<tr align=center>
|
|
<td colspan=4>Location of Grid Points in Dimension #1</td>
|
|
<tr align=center>
|
|
<td colspan=4>.<br>.<br>.<br></td>
|
|
<tr align=center>
|
|
<td colspan=4>Location of Grid Points in Dimension #n</td>
|
|
</table>
|
|
</center>
|
|
|
|
<P>
|
|
<center>
|
|
<table border cellpadding=4 width="80%">
|
|
<caption align=bottom>
|
|
<B>HDF5 Dataspace Unstructured Grid Information</B>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
|
|
<tr align=center>
|
|
<td colspan=4># of Grid Points</td>
|
|
<tr align=center>
|
|
<td colspan=4>Datatype of Grid Point Locations</td>
|
|
<tr align=center>
|
|
<td colspan=4>Grid Point Locations<br>.<br>.<br></td>
|
|
</table>
|
|
</center>
|
|
-->
|
|
|
|
<hr>
|
|
<h4><a name="ReservedMessage_0002">Name: Reserved - Not Assigned Yet</a></h4>
|
|
<b>Header Message Type:</b> 0x0002<BR>
|
|
<b>Length:</b> N/A<BR>
|
|
<b>Status:</b> N/A<BR>
|
|
<b>Format of Data:</b> N/A<BR>
|
|
|
|
<p><b>Purpose and Description:</b> This message type was skipped during
|
|
the initial specification of the file format and may be used in a
|
|
future expansion to the format.
|
|
|
|
|
|
<hr>
|
|
<h4><a name="DataTypeMessage">Name: Datatype</a></h4>
|
|
|
|
<P class=item><B>Header Message Type:</B> 0x0003
|
|
</P>
|
|
<P class=item><B>Length:</B> variable
|
|
</P>
|
|
<P class=item><B>Status:</B> Required for dataset or named datatype objects,
|
|
may not be repeated.
|
|
</P>
|
|
|
|
<P class=item><B>Description:</B> The datatype message defines the datatype
|
|
for each element of a dataset. A datatype can describe an atomic type
|
|
like a fixed- or floating-point type or a compound type like a C
|
|
struct.
|
|
Datatypes messages are stored
|
|
as a list of datatype classes and
|
|
their associated properties.
|
|
</P>
|
|
|
|
<P class=item2>Datatype messages that are part of a dataset object,
|
|
do not describe how elements are related to one another, the dataspace
|
|
message is used for that purpose. Datatype messages that are part of
|
|
a named datatype message describe an "abstract" datatype that can be
|
|
used by other objects in the file.
|
|
</P>
|
|
|
|
<P class=item><B>Format of Data:</B>
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Datatype Message
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Class and Version</td>
|
|
<td>Class Bit Field, Bits 0-7</td>
|
|
<td>Class Bit Field, Bits 8-15</td>
|
|
<td>Class Bit Field, Bits 16-23</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Size</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br><br>Properties<br><br><br></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Class and Version</td>
|
|
<td>
|
|
<P>The version of the datatype message and the datatype's class
|
|
information are packed together in this field. The version
|
|
number is packed in the top 4 bits of the field and the class
|
|
is contained in the bottom 4 bits.
|
|
</P>
|
|
<P>The version number information is used for changes in the
|
|
format of the datatype message and is described here:
|
|
<table class=list>
|
|
<tr>
|
|
<th width="30%">Version</th>
|
|
<th align=left>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>0</code></td>
|
|
<td>Never used
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td align=center><code>1</code></td>
|
|
<td>Used by early versions of the library to encode
|
|
compound datatypes with explicit array fields.
|
|
See the compound datatype description below for
|
|
further details.
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td align=center><code>2</code></td>
|
|
<td>The current version used by the library.
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</P>
|
|
<P>The class of the datatype determines the format for the class
|
|
bit field and properties portion of the datatype message, which
|
|
are described below. The
|
|
following classes are currently defined:
|
|
<table width=100% class=list>
|
|
<tr>
|
|
<th width="30%">Value</th>
|
|
<th align=left>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>0</code></td>
|
|
<td>Fixed-Point</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>1</code></td>
|
|
<td>Floating-Point</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>2</code></td>
|
|
<td>Time</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>3</code></td>
|
|
<td>String</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>4</code></td>
|
|
<td>Bitfield</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>5</code></td>
|
|
<td>Opaque</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>6</code></td>
|
|
<td>Compound</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>7</code></td>
|
|
<td>Reference</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>8</code></td>
|
|
<td>Enumerated</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>9</code></td>
|
|
<td>Variable-Length</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>10</code></td>
|
|
<td>Array</td>
|
|
</tr>
|
|
</table>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Class Bit Fields</td>
|
|
<td>
|
|
<P>The information in these bit fields is specific to each datatype
|
|
class and is described below. All bits not defined for a
|
|
datatype class are set to zero.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Size</td>
|
|
<td>
|
|
<P>The size of the datatype in bytes.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Properties</td>
|
|
<td>
|
|
<P>This variable-sized field encodes information specific to each
|
|
datatype class and is described below. If there is no
|
|
property information specified for a datatype class, the size
|
|
of this field is zero.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
</div>
|
|
</P>
|
|
|
|
<P>Class specific information for Fixed-Point Numbers (Class 0):
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<caption>
|
|
Bit Field Description
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="10%">Bits</th>
|
|
<th>Meaning</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>0</td>
|
|
<td><b>Byte Order.</b> If zero, byte order is little-endian;
|
|
otherwise, byte order is big endian.</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>1, 2</td>
|
|
<td><b>Padding type.</b> Bit 1 is the lo_pad type and bit 2
|
|
is the hi_pad type. If a datum has unused bits at either
|
|
end, then the lo_pad or hi_pad bit is copied to those
|
|
locations.</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>3</td>
|
|
<td><b>Signed.</b> If this bit is set then the fixed-point
|
|
number is in 2's complement form.</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>4-23</td>
|
|
<td>Reserved (zero).</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Property Descriptions
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=2>Bit Offset</td>
|
|
<td colspan=2>Bit Precision</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Bit Offset</td>
|
|
<td>
|
|
<P>The bit offset of the first significant bit of the fixed-point
|
|
value within the datatype. The bit offset specifies the number
|
|
of bits "to the right of" the value.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Bit Precision</td>
|
|
<td>
|
|
<P>The number of bits of precision of the fixed-point value
|
|
within the datatype.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
</div>
|
|
</P>
|
|
|
|
<P>Class specific information for Floating-Point Numbers (Class 1):
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<caption>
|
|
Bit Field Description
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="10%">Bits</th>
|
|
<th>Meaning</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>0</td>
|
|
<td><b>Byte Order.</b> If zero, byte order is little-endian;
|
|
otherwise, byte order is big endian.</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>1, 2, 3</td>
|
|
<td><b>Padding type.</b> Bit 1 is the low bits pad type, bit 2
|
|
is the high bits pad type, and bit 3 is the internal bits
|
|
pad type. If a datum has unused bits at either end or between
|
|
the sign bit, exponent, or mantissa, then the value of bit
|
|
1, 2, or 3 is copied to those locations.</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>4-5</td>
|
|
<td><b>Normalization.</b> The value can be 0 if there is no
|
|
normalization, 1 if the most significant bit of the
|
|
mantissa is always set (except for 0.0), and 2 if the most
|
|
signficant bit of the mantissa is not stored but is
|
|
implied to be set. The value 3 is reserved and will not
|
|
appear in this field.</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>6-7</td>
|
|
<td>Reserved (zero).</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>8-15</td>
|
|
<td><b>Sign Location.</b> This is the bit position of the sign
|
|
bit. Bits are numbered with the least significant bit zero.</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>16-23</td>
|
|
<td>Reserved (zero).</td>
|
|
</tr>
|
|
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Property Descriptions
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=2>Bit Offset</td>
|
|
<td colspan=2>Bit Precision</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Exponent Location</td>
|
|
<td>Exponent Size</td>
|
|
<td>Mantissa Location</td>
|
|
<td>Mantissa Size</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Exponent Bias</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Bit Offset</td>
|
|
<td>
|
|
<P>The bit offset of the first significant bit of the floating-point
|
|
value within the datatype. The bit offset specifies the number
|
|
of bits "to the right of" the value.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Bit Precision</td>
|
|
<td>
|
|
<P>The number of bits of precision of the floating-point value
|
|
within the datatype.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Exponent Location</td>
|
|
<td>
|
|
<P>The bit position of the exponent field. Bits are numbered with
|
|
the least significant bit number zero.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Exponent Size</td>
|
|
<td>
|
|
<P>The size of the exponent field in bits.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Mantissa Location</td>
|
|
<td>
|
|
<P>The bit position of the mantissa field. Bits are numbered with
|
|
the least significant bit number zero.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Mantissa Size</td>
|
|
<td>
|
|
<P>The size of the mantissa field in bits.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Exponent Bias</td>
|
|
<td>
|
|
<P>The bias of the exponent field.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
</div>
|
|
</P>
|
|
|
|
<P>Class specific information for Time (Class 2):
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<caption>
|
|
Bit Field Description
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="10%">Bits</th>
|
|
<th>Meaning</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>0</td>
|
|
<td><b>Byte Order.</b> If zero, byte order is little-endian;
|
|
otherwise, byte order is big endian.</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>1-23</td>
|
|
<td>Reserved (zero).</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Property Descriptions
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=2>Bit Precision</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Bit Precision</td>
|
|
<td>
|
|
<P>The number of bits of precision of the time value.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
</div>
|
|
</P>
|
|
|
|
<P>Class specific information for Strings (Class 3):
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<caption>
|
|
Bit Field Description
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="10%">Bits</th>
|
|
<th>Meaning</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>0-3</td>
|
|
<td><b>Padding type.</b> This four-bit value determines the
|
|
type of padding to use for the string. The values are:
|
|
|
|
<table width=100% class=list>
|
|
<tr>
|
|
<th width="30%">Value</th>
|
|
<th align=left>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>0</code></td>
|
|
<td>Null Terminate: A zero byte marks the end of the
|
|
string and is guaranteed to be present after
|
|
converting a long string to a short string. When
|
|
converting a short string to a long string the value is
|
|
padded with additional null characters as necessary.
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>1</code></td>
|
|
<td>Null Pad: Null characters are added to the end of
|
|
the value during conversions from short values to long
|
|
values but conversion in the opposite direction simply
|
|
truncates the value.
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>2</code></td>
|
|
<td>Space Pad: Space characters are added to the end of
|
|
the value during conversions from short values to long
|
|
values but conversion in the opposite direction simply
|
|
truncates the value. This is the Fortran
|
|
representation of the string.
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>3-15</code></td>
|
|
<td>Reserved
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>4-7</td>
|
|
<td><b>Character Set.</b> The character set to use for
|
|
encoding the string. The only character set supported is
|
|
the 8-bit ASCII (zero) so no translations have been defined
|
|
yet.</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>8-23</td>
|
|
<td>Reserved (zero).</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<P>There are no properties defined for the string class.
|
|
</P>
|
|
</P>
|
|
|
|
<P>Class specific information for Bitfields (Class 4):
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<caption>
|
|
Bit Field Description
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="10%">Bits</th>
|
|
<th>Meaning</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>0</td>
|
|
<td><b>Byte Order.</b> If zero, byte order is little-endian;
|
|
otherwise, byte order is big endian.</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>1, 2</td>
|
|
<td><b>Padding type.</b> Bit 1 is the lo_pad type and bit 2
|
|
is the hi_pad type. If a datum has unused bits at either
|
|
end, then the lo_pad or hi_pad bit is copied to those
|
|
locations.</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>3-23</td>
|
|
<td>Reserved (zero).</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Property Description
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=2>Bit Offset</td>
|
|
<td colspan=2>Bit Precision</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Bit Offset</td>
|
|
<td>
|
|
<P>The bit offset of the first significant bit of the bitfield
|
|
within the datatype. The bit offset specifies the number
|
|
of bits "to the right of" the value.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Bit Precision</td>
|
|
<td>
|
|
<P>The number of bits of precision of the bitfield
|
|
within the datatype.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
</P>
|
|
|
|
<P>Class specific information for Opaque (Class 5):
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<caption>
|
|
Bit Field Description
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="10%">Bits</th>
|
|
<th>Meaning</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>0-7</td>
|
|
<td>Length of ASCII tag in bytes.</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>8-23</td>
|
|
<td>Reserved (zero).</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Property Description
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>ASCII Tag<br>
|
|
<br></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>ASCII Tag</td>
|
|
<td>
|
|
<P>This NUL-terminated string provides a description for the
|
|
opaque type. It is NUL-padded to a multiple of 8 bytes.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
</P>
|
|
|
|
<P>Class specific information for Compound (Class 6):
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<caption>
|
|
Bit Field Description
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="10%">Bits</th>
|
|
<th>Meaning</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>0-15</td>
|
|
<td><b>Number of Members.</b> This field contains the number
|
|
of members defined for the compound datatype. The member
|
|
definitions are listed in the Properties field of the data
|
|
type message.
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>15-23</td>
|
|
<td>Reserved (zero).</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
</P>
|
|
|
|
<P>The Properties field of a compound datatype is a list of the
|
|
member definitions of the compound datatype. The member
|
|
definitions appear one after another with no intervening bytes.
|
|
The member types are described with a recursive datatype
|
|
message.
|
|
|
|
<P>Note that the property descriptions are different for different
|
|
versions of the datatype version. Additionally note that the version
|
|
0 properties are deprecated and have been replaced with the version
|
|
1 properties in versions of the HDF5 library from the 1.4 release
|
|
onward.
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Properties Description for Datatype Version 1
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>Name<br><br></td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Byte Offset of Member</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Dimensionality</td>
|
|
<td colspan=3>Reserved (zero)</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Dimension Permutation</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Reserved (zero)</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Dimension #1 Size (required)</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Dimension #2 Size (required)</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Dimension #3 Size (required)</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Dimension #4 Size (required)</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>Member Type Message<br><br></td>
|
|
</tr>
|
|
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Name</td>
|
|
<td>
|
|
<P>This NUL-terminated string provides a description for the
|
|
opaque type. It is NUL-padded to a multiple of 8 bytes.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Byte Offset of Member</td>
|
|
<td>
|
|
<P>This is the byte offset of the member within the datatype.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Dimensionality</td>
|
|
<td>
|
|
<P>If set to zero, this field indicates a scalar member. If set
|
|
to a value greater than zero, this field indicates that the
|
|
member is an array of values. For array members, the size of
|
|
the array is indicated by the 'Size of Dimension n' field in
|
|
this message.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Dimension Permutation</td>
|
|
<td>
|
|
<P>This field was intended to allow an array field to have
|
|
it's dimensions permuted, but this was never implemented.
|
|
This field should always be set to zero.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Dimension #n Size</td>
|
|
<td>
|
|
<P>This field is the size of a dimension of the array field as
|
|
stored in the file. The first dimension stored in the list of
|
|
dimensions is the slowest changing dimension and the last
|
|
dimension stored is the fastest changing dimension.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Member Type Message</td>
|
|
<td>
|
|
<P>This field is a datatype message describing the datatype of
|
|
the member.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Properties Description for Datatype Version 2
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>Name<br><br></td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Byte Offset of Member</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>Member Type Message<br><br></td>
|
|
</tr>
|
|
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Name</td>
|
|
<td>
|
|
<P>This NUL-terminated string provides a description for the
|
|
opaque type. It is NUL-padded to a multiple of 8 bytes.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Byte Offset of Member</td>
|
|
<td>
|
|
<P>This is the byte offset of the member within the datatype.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Member Type Message</td>
|
|
<td>
|
|
<P>This field is a datatype message describing the datatype of
|
|
the member.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
</div>
|
|
</P>
|
|
|
|
<P>Class specific information for Reference (Class 7):
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<caption>
|
|
Bit Field Description
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="10%">Bits</th>
|
|
<th>Meaning</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>0-3</td>
|
|
<td><b>Type.</b> This four-bit value contains the type of reference
|
|
described. The values defined are:
|
|
|
|
<table width=100% class=list>
|
|
<tr>
|
|
<th width="30%">Value</th>
|
|
<th align=left>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>0</code></td>
|
|
<td>Object Reference: A reference to another object in this
|
|
HDF5 file.
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>1</code></td>
|
|
<td>Dataset Region Reference: A reference to a region within
|
|
a dataset in this HDF5 file.
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>2</code></td>
|
|
<td>Internal Reference: A reference to a region within the
|
|
current dataset. (Not currently implemented)
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>3-15</code></td>
|
|
<td>Reserved
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>15-23</td>
|
|
<td>Reserved (zero).</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<P>There are no properties defined for the reference class.
|
|
</P>
|
|
</P>
|
|
|
|
<P>Class specific information for Enumeration (Class 8):
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<caption>
|
|
Bit Field Description
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="10%">Bits</th>
|
|
<th>Meaning</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>0-15</td>
|
|
<td><b>Number of Members.</b> The number of name/value
|
|
pairs defined for the enumeration type.</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>16-23</td>
|
|
<td>Reserved (zero).</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Property Description
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>Base Type<br><br></td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>Names<br><br></td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>Values<br><br></td>
|
|
</tr>
|
|
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Base Type</td>
|
|
<td>
|
|
<P>Each enumeration type is based on some parent type, usually an
|
|
integer. The information for that parent type is described
|
|
recursively by this field.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Names</td>
|
|
<td>
|
|
<P>The name for each name/value pair. Each name is stored as a null
|
|
terminated ASCII string in a multiple of eight bytes. The names
|
|
are in no particular order.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Values</td>
|
|
<td>
|
|
<P>The list of values in the same order as the names. The values
|
|
are packed (no inter-value padding) and the size of each value
|
|
is determined by the parent type.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
</div>
|
|
</P>
|
|
|
|
|
|
<P>Class specific information for Variable-Length (Class 9):
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<caption>
|
|
Bit Field Description
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="10%">Bits</th>
|
|
<th>Meaning</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>0-3</td>
|
|
<td><b>Type.</b> This four-bit value contains the type of
|
|
variable-length datatype described. The values defined are:
|
|
|
|
<table width=100% class=list>
|
|
<tr>
|
|
<th width="30%">Value</th>
|
|
<th align=left>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>0</code></td>
|
|
<td>Sequence: A variable-length sequence of any sequence of
|
|
data. Variable-length sequences do not have padding or
|
|
character set information.
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>1</code></td>
|
|
<td>String: A variable-length sequence of characters.
|
|
Variable-length strings have padding and character set
|
|
information.
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>2-15</code></td>
|
|
<td>Reserved
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>4-7</td>
|
|
<td><b>Padding type.</b> (variable-length string only)
|
|
This four-bit value determines the type of padding
|
|
used for variable-length strings. The values are the same
|
|
as for the string padding type, as follows:
|
|
<table width=100% class=list>
|
|
<tr>
|
|
<th width="30%">Value</th>
|
|
<th align=left>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>0</code></td>
|
|
<td>Null terminate: A zero byte marks the end of a string
|
|
and is guaranteed to be present after converting a long
|
|
string to a short string. When converting a short string
|
|
to a long string, the value is padded with additional null
|
|
characters as necessary.
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>1</code></td>
|
|
<td>Null pad: Null characters are added to the end of the
|
|
value during conversion from a short string to a longer
|
|
string. Conversion from a long string to a shorter string
|
|
simply truncates the value.
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>2</code></td>
|
|
<td>Space pad: Space characters are added to the end of the
|
|
value during conversion from a short string to a longer
|
|
string. Conversion from a long string to a shorter string
|
|
simply truncates the value. This is the Fortran
|
|
representation of the string.
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>3-15</code></td>
|
|
<td>Reserved
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
This value is set to zero for variable-length sequences.
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>8-11</td>
|
|
<td><b>Character Set.</b> (variable-length string only)
|
|
This four-bit value specifies the character set
|
|
to be used for encoding the string:
|
|
<table width=100% class=list>
|
|
<tr>
|
|
<th width="30%">Value</th>
|
|
<th align=left>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>0</code></td>
|
|
<td>ASCII: As of this writing (July 2003, Release 1.6.0),
|
|
8-bit ASCII is the only character set supported. Therefore,
|
|
no translations have been defined.
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>1-15</code></td>
|
|
<td>Reserved
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
This value is set to zero for variable-length sequences.
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>12-23</td>
|
|
<td>Reserved (zero).</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Property Description
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>Base Type<br><br></td>
|
|
</tr>
|
|
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Base Type</td>
|
|
<td>
|
|
<P>Each variable-length type is based on some parent type. The
|
|
information for that parent type is described recursively by
|
|
this field.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
</div>
|
|
</P>
|
|
|
|
<P>Class specific information for Array (Class 10):
|
|
|
|
<P>There are no bit fields defined for the array class.
|
|
</P>
|
|
|
|
<P>Note that the dimension information defined in the property for this
|
|
datatype class is independent of dataspace information for a dataset.
|
|
The dimension information here describes the dimensionality of the
|
|
information within a data element (or a component of an element, if the
|
|
array datatype is nested within another datatype) and the dataspace for a
|
|
dataset describes the location of the elements in a dataset.
|
|
</P>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Property Description
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
<th width="25%">Byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Dimensionality</td>
|
|
<td colspan=3>Reserved (zero)</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Dimension #1 Size</td>
|
|
</tr>
|
|
<tr>
|
|
<td colspan=4>.<br>.<br>.<br></td>
|
|
</tr>
|
|
<tr>
|
|
<td colspan=4>Dimension #n Size</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Permutation Index #1</td>
|
|
</tr>
|
|
<tr>
|
|
<td colspan=4>.<br>.<br>.<br></td>
|
|
</tr>
|
|
<tr>
|
|
<td colspan=4>Permutation Index #n</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>Base Type<br><br></td>
|
|
</tr>
|
|
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Dimensionality</td>
|
|
<td>
|
|
<P>This value is the number of dimensions that the array has.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Dimension #n Size</td>
|
|
<td>
|
|
<P>This value is the size of the dimension of the array
|
|
as stored in the file. The first dimension stored in
|
|
the list of dimensions is the slowest changing dimension
|
|
and the last dimension stored is the fastest changing
|
|
dimension.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Permutation Index #n</td>
|
|
<td>
|
|
<P>This value is the index permutation used to map
|
|
each dimension from the canonical representation to an
|
|
alternate axis for each dimension. Currently, dimension
|
|
permutations are not supported and these indices should be set
|
|
to the index position minus one (i.e. the first dimension should
|
|
be set to 0, the second dimension should be set to 1, etc.)
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Base Type</td>
|
|
<td>
|
|
<P>Each array type is based on some parent type. The
|
|
information for that parent type is described recursively by
|
|
this field.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
</div>
|
|
|
|
</P>
|
|
|
|
<hr>
|
|
<h4><a name="OldFillValueMessage">Name: Data Storage - Fill Value (Old)</a></h4>
|
|
|
|
<P class=item><B>Header Message Type:</B> 0x0004
|
|
</P>
|
|
<P class=item><B>Length:</B> varies
|
|
</P>
|
|
<P class=item><B>Status:</B> Optional, may not be repeated.
|
|
</P>
|
|
|
|
<P class=item><B>Description:</B> The fill value message stores a single
|
|
data value which is returned to the application when an uninitialized
|
|
data element is read from a dataset. The fill value is interpreted
|
|
with the same datatype as the dataset. If no fill value message is
|
|
present then a fill value of all zero bytes is assumed.
|
|
</P>
|
|
|
|
<P class=item2>This fill value message is deprecated in favor of the "new"
|
|
fill value message (Message Type 0x0005) and is only written to the
|
|
file for forward compatibility with versions of the HDF5 library before
|
|
the 1.6.0 version. Additionally, it only appears for datasets with a
|
|
user defined fill value (as opposed to the library default fill value
|
|
or an explicitly set "undefined" fill value).
|
|
</P>
|
|
|
|
<P class=item><B>Format of Data:</B>
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Fill Value Message (Old)
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Size</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>Fill Value<br><br></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Size</td>
|
|
<td>
|
|
<P>This is the size of the Fill Value field in bytes.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Fill Value</td>
|
|
<td>
|
|
<P>The fill value. The bytes of the fill value are interpreted
|
|
using the same datatype as for the dataset.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
</P>
|
|
|
|
<hr>
|
|
<h4><a name="FillValueMessage">Name: Data Storage - Fill Value </a></h4>
|
|
|
|
<P class=item><B>Header Message Type:</B> 0x0005
|
|
</P>
|
|
<P class=item><B>Length:</B> varies
|
|
</P>
|
|
<P class=item><B>Status:</B> Required for dataset objects, may not be repeated.
|
|
</P>
|
|
|
|
<P class=item><B>Description:</B> The fill value message stores a single
|
|
data value which is returned to the application when an uninitialized
|
|
data element is read from a dataset. The fill value is interpreted
|
|
with the same datatype as the dataset.
|
|
</P>
|
|
|
|
<P class=item><B>Format of Data:</B>
|
|
<br>
|
|
<div align=center>
|
|
<table class=format>
|
|
<caption>
|
|
Fill Value Message
|
|
</caption>
|
|
|
|
<tr>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Version</td>
|
|
<td>Space Allocation Time</td>
|
|
<td>Fill Value Write Time</td>
|
|
<td>Fill Value Defined</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4>Size</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td colspan=4><br>Fill Value<br><br></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<br>
|
|
<div align=center>
|
|
<table class=desc>
|
|
<tr>
|
|
<th width="30%">Field Name</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Version</td>
|
|
<td>
|
|
<P>The version number information is used for changes in the
|
|
format of the fill value message and is described here:
|
|
<table class=list>
|
|
<tr>
|
|
<th width="30%">Version</th>
|
|
<th align=left>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>0</code></td>
|
|
<td>Never used
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td align=center><code>1</code></td>
|
|
<td>Used by version 1.6.x of the library to encode
|
|
fill values. In this version, the Size field is
|
|
always present.
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td align=center><code>2</code></td>
|
|
<td>The current version used by the library (version
|
|
1.7.3 or later). In this version, the Size and
|
|
Fill Value fields are
|
|
only present if the Fill Value Defined field is set
|
|
to 1.
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Space Allocation Time</td>
|
|
<td>
|
|
<P>When the storage space for the dataset's raw data will be
|
|
allocated. The allowed values are:
|
|
<table class=list>
|
|
<tr>
|
|
<th width="30%">Value</th>
|
|
<th align=left>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>1</code></td>
|
|
<td>Early allocation. Storage space for the entire dataset
|
|
should be allocated in the file when the dataset is
|
|
created.
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td align=center><code>2</code></td>
|
|
<td>Late allocation. Storage space for the entire dataset
|
|
should not be allocated until the dataset is written
|
|
to.
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td align=center><code>3</code></td>
|
|
<td>Incremental allocation. Storage space for the
|
|
dataset should not be allocated until the portion
|
|
of the dataset is written to. This is currently
|
|
used in conjunction with chunked data storage for
|
|
datasets.
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Fill Value Write Time</td>
|
|
<td>
|
|
<P>At the time that storage space for the dataset's raw data is
|
|
allocated, this value indicates whether the fill value should
|
|
be written to the raw data storage elements. The allowed values
|
|
are:
|
|
<table class=list>
|
|
<tr>
|
|
<th width="30%">Value</th>
|
|
<th align=left>Description</th>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td align=center><code>0</code></td>
|
|
<td>On allocation. The fill value is always written to
|
|
the raw data storage when the storage space is allocated.
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td align=center><code>1</code></td>
|
|
<td>Never. The fill value should never be written to
|
|
the raw data storage.
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td align=center><code>2</code></td>
|
|
<td>Fill value written if set by user. The fill value
|
|
will be written to the raw data storage when the storage
|
|
space is allocated only if the user explicitly set
|
|
the fill value. If the fill value is the library
|
|
default or is undefined, it will not be written to
|
|
the raw data storage.
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Fill Value Defined</td>
|
|
<td>
|
|
<P>This value indicates if a fill value is defined for this
|
|
dataset. If this value is 0, the fill value is undefined.
|
|
If this value is 1, a fill value is defined for this dataset.
|
|
For version 2 or later of the fill value message, this value
|
|
controls the presence of the Size field.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Size</td>
|
|
<td>
|
|
<P>This is the size of the Fill Value field in bytes. This field
|
|
is not present if the Version field is >1 and the Fill Value
|
|
Defined field is set to 0.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td>Fill Value</td>
|
|
<td>
|
|
<P>The fill value. The bytes of the fill value are interpreted
|
|
using the same datatype as for the dataset. This field is
|
|
not present if the Version field is >1 and the Fill Value
|
|
Defined field is set to 0.
|
|
</P>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
</P>
|
|
|
|
<!--
|
|
<hr>
|
|
<h4><a name="CompactDataStorageMessage">Name: Data Storage - Compact</a></h4>
|
|
|
|
<b>Header Message Type:</b> 0x0006<br>
|
|
<b>Length:</b> varies<br>
|
|
<b>Status:</b> Optional, may not be repeated.<br>
|
|
|
|
<p>This message indicates that the data for the data object is
|
|
stored within the current HDF file by including the actual
|
|
data as the header data for this message. The data is
|
|
stored internally in
|
|
the <em>normal format</em>, i.e. in one chunk, uncompressed, etc.
|
|
|
|
<P>Note that one and only one of the <em>Data Storage</em> headers can be
|
|
stored for each data object.
|
|
|
|
<P><b>Format of Data:</b> The message data is actually composed
|
|
of dataset data, so the format will be determined by the dataset
|
|
format.
|
|
-->
|
|
|
|
<hr>
|
|
<h4><a name="ReservedMessage_0006">Name: Reserved - Not Assigned Yet</a></h4>
|
|
<b>Header Message Type:</b> 0x0006<BR>
|
|
<b>Length:</b> N/A<BR>
|
|
<b>Status:</b> N/A<BR>
|
|
<b>Format of Data:</b> N/A<BR>
|
|
|
|
<p><b>Purpose and Description:</b> This message type was skipped during
|
|
the initial specification of the file format and may be used in a
|
|
future expansion to the format.
|
|
|
|
<hr>
|
|
<h4><a name="ExternalFileListMessage">Name: Data Storage -
|
|
External Data Files</a></h4>
|
|
<b>Header Message Type:</b> 0x0007<BR>
|
|
<b>Length:</b> varies<BR>
|
|
<b>Status:</b> Optional, may not be repeated.<BR>
|
|
|
|
<p><b>Purpose and Description:</b> The external object message
|
|
indicates that the data for an object is stored outside the HDF5
|
|
file. The filename of the object is stored as a Universal
|
|
Resource Location (URL) of the actual filename containing the
|
|
data. An external file list record also contains the byte offset
|
|
of the start of the data within the file and the amount of space
|
|
reserved in the file for that data.
|
|
|
|
<p>
|
|
<center>
|
|
<table border cellpadding=4 width="80%">
|
|
<caption align=top>
|
|
<b>External File List Message</b>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td>Version</td>
|
|
<td colspan=3>Reserved</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=2>Allocated Slots</td>
|
|
<td colspan=2>Used Slots</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4><br>Heap Address<br><br></td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4><br>Slot Definitions...<br><br></td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<center>
|
|
<table align=center width="80%">
|
|
<tr align=left>
|
|
<th width="30%"><U><font size=+1>Field Name</font></U></th>
|
|
<th><U><font size=+1>Description</font></U></th>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Version </td>
|
|
<td>This value is used to determine the format of the
|
|
External File List Message. When the format of the
|
|
information in the message is changed, the version number
|
|
is incremented and can be used to determine how the
|
|
information in the object header is formatted.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Reserved</td>
|
|
<td>This field is reserved for future use.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Allocated Slots</td>
|
|
<td>The total number of slots allocated in the message. Its
|
|
value must be at least as large as the value contained in
|
|
the Used Slots field.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Used Slots</td>
|
|
<td>The number of initial slots which contain valid
|
|
information. The remaining slots are zero filled.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Heap Address</td>
|
|
<td>This is the address of a local name heap which contains
|
|
the names for the external files. The name at offset zero
|
|
in the heap is always the empty string.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Slot Definitions</td>
|
|
<td>The slot definitions are stored in order according to
|
|
the array addresses they represent. If more slots have
|
|
been allocated than what has been used then the defined
|
|
slots are all at the beginning of the list.</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<center>
|
|
<table border cellpadding=4 width="80%">
|
|
<caption align=top>
|
|
<b>External File List Slot</b>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4><br>Name Offset (<size> bytes)<br><br></td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4><br>File Offset (<size> bytes)<br><br></td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4><br>Size<br><br></td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<center>
|
|
<table align=center width="80%">
|
|
<tr align=left>
|
|
<th width="30%"><U><font size=+1>Field Name</font></U></th>
|
|
<th><U><font size=+1>Description</font></U></th>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Name Offset (<size> bytes)</td>
|
|
<td>The byte offset within the local name heap for the name
|
|
of the file. File names are stored as a URL which has a
|
|
protocol name, a host name, a port number, and a file
|
|
name:
|
|
<code><em>protocol</em>:<em>port</em>//<em>host</em>/<em>file</em></code>.
|
|
If the protocol is omitted then "file:" is assumed. If
|
|
the port number is omitted then a default port for that
|
|
protocol is used. If both the protocol and the port
|
|
number are omitted then the colon can also be omitted. If
|
|
the double slash and host name are omitted then
|
|
"localhost" is assumed. The file name is the only
|
|
mandatory part, and if the leading slash is missing then
|
|
it is relative to the application's current working
|
|
directory (the use of relative names is not
|
|
recommended).</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>File Offset (<size> bytes)</td>
|
|
<td>This is the byte offset to the start of the data in the
|
|
specified file. For files that contain data for a single
|
|
dataset this will usually be zero.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Size</td>
|
|
<td>This is the total number of bytes reserved in the
|
|
specified file for raw data storage. For a file that
|
|
contains exactly one complete dataset which is not
|
|
extendable, the size will usually be the exact size of the
|
|
dataset. However, by making the size larger one allows
|
|
HDF5 to extend the dataset. The size can be set to a value
|
|
larger than the entire file since HDF5 will read zeros
|
|
past the end of the file without failing.</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
|
|
<hr>
|
|
<h4><a name="LayoutMessage">Name: Data Storage - Layout</a></h4>
|
|
|
|
<b>Header Message Type:</b> 0x0008<BR>
|
|
<b>Length:</b> varies<BR>
|
|
<b>Status:</b> Required for datasets, may not be repeated.
|
|
|
|
<p><b>Purpose and Description:</b> Data layout describes how the
|
|
elements of a multi-dimensional array are arranged in the linear
|
|
address space of the file. Three types of data layout are
|
|
supported:
|
|
|
|
<ol>
|
|
<li>The array can be stored in one contiguous area of the file.
|
|
The layout requires that the size of the array be constant and
|
|
does not permit chunking, compression, checksums, encryption,
|
|
etc. The message stores the total size of the array and the
|
|
offset of an element from the beginning of the storage area is
|
|
computed as in C.
|
|
|
|
<li>The array domain can be regularly decomposed into chunks and
|
|
each chunk is allocated separately. This layout supports
|
|
arbitrary element traversals, compression, encryption, and
|
|
checksums, and the chunks can be distributed across external
|
|
raw data files (these features are described in other
|
|
messages). The message stores the size of a chunk instead of
|
|
the size of the entire array; the size of the entire array can
|
|
be calculated by traversing the B-tree that stores the chunk
|
|
addresses.
|
|
|
|
<li>The array can be stored in one contiguous block, as part of
|
|
this object header message (this is called "compact" storage below).
|
|
</ol>
|
|
|
|
<P>Version 3 of this message re-structured the format into specific
|
|
properties that are required for each layout class.
|
|
|
|
<p>
|
|
<center>
|
|
<table border cellpadding=4 width="80%">
|
|
<caption align=top>
|
|
<B>Data Layout Message, Versions 1 and 2</B>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td>Version</td>
|
|
<td>Dimensionality</td>
|
|
<td>Layout Class</td>
|
|
<td>Reserved</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Reserved</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4><br>Address<br><br></td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Dimension 0 (4-bytes)</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Dimension 1 (4-bytes)</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>...</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Compact Data Size (4-bytes)</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Compact Data</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>...</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<center>
|
|
<table align=center width="80%">
|
|
<tr align=left>
|
|
<th width="30%"><U><font size=+1>Field Name</font></U></th>
|
|
<th><U><font size=+1>Description</font></U></th>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Version</td>
|
|
<td>A version number for the layout message. This value can be
|
|
either 1 or 2.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Dimensionality</td>
|
|
<td>An array has a fixed dimensionality. This field
|
|
specifies the number of dimension size fields later in the
|
|
message.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Layout Class</td>
|
|
<td>The layout class specifies how the other fields of the
|
|
layout message are to be interpreted. A value of one
|
|
indicates contiguous storage, a value of two
|
|
indicates chunked storage,
|
|
while a value of zero
|
|
indicates compact storage. Other values will be defined
|
|
in the future.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Address</td>
|
|
<td>For contiguous storage, this is the address of the first
|
|
byte of storage. For chunked storage this is the address
|
|
of the B-tree that is used to look up the addresses of the
|
|
chunks. This field is not present for compact storage.
|
|
If the version for this message is set to 2, the address
|
|
may have the "undefined address" value, to indicate that
|
|
storage has not yet been allocated for this array.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Dimensions</td>
|
|
<td>For contiguous storage the dimensions define the entire
|
|
size of the array while for chunked storage they define
|
|
the size of a single chunk.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Compact Data Size</td>
|
|
<td>This field is only present for compact data storage.
|
|
It contains the size of the raw data for the dataset array.</td>
|
|
|
|
<tr valign=top>
|
|
<td>Compact Data</td>
|
|
<td>This field is only present for compact data storage.
|
|
It contains the raw data for the dataset array.</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<center>
|
|
<table border cellpadding=4 width="80%">
|
|
<caption align=top>
|
|
<B>Data Layout Message, Version 3</B>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td>Version</td>
|
|
<td>Layout Class</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Properties</td>
|
|
</tr>
|
|
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<center>
|
|
<table align=center width="80%">
|
|
<tr align=left>
|
|
<th width="30%"><U><font size=+1>Field Name</font></U></th>
|
|
<th><U><font size=+1>Description</font></U></th>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Version</td>
|
|
<td>A version number for the layout message. This value can be
|
|
either 1, 2 or 3.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Layout Class</td>
|
|
<td>The layout class specifies how the other fields of the
|
|
layout message are to be interpreted. A value of one
|
|
indicates contiguous storage, a value of two
|
|
indicates chunked storage,
|
|
while a value of three
|
|
indicates compact storage.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Properties</td>
|
|
<td>This variable-sized field encodes information specific to each
|
|
layout class and is described below. If there is no property
|
|
information specified for a layout class, the size of this field
|
|
is zero bytes.</td>
|
|
</tr>
|
|
|
|
</table>
|
|
</center>
|
|
|
|
<P>Class-specific information for contiguous layout (Class 0):
|
|
|
|
<p>
|
|
<center>
|
|
<table border cellpadding=4 width="80%">
|
|
<caption align=top>
|
|
<B>Property Descriptions</B>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4><br>Address<br><br></td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4><br>Size<br><br></td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<center>
|
|
<table align=center width="80%">
|
|
<tr align=left>
|
|
<th width="30%"><U><font size=+1>Field Name</font></U></th>
|
|
<th><U><font size=+1>Description</font></U></th>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Address</td>
|
|
<td>This is the address of the first byte of raw data storage.
|
|
The address may have the "undefined address" value, to indicate
|
|
that storage has not yet been allocated for this array.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Size</td>
|
|
<td>This field contains the size allocated to store the raw data.</td>
|
|
</table>
|
|
</center>
|
|
|
|
<P>Class-specific information for chunked layout (Class 1):
|
|
|
|
<p>
|
|
<center>
|
|
<table border cellpadding=4 width="80%">
|
|
<caption align=top>
|
|
<B>Property Descriptions</B>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td>Dimensionality</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4><br>Address<br><br></td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Dimension 0 (4-bytes)</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Dimension 1 (4-bytes)</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>...</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<center>
|
|
<table align=center width="80%">
|
|
<tr align=left>
|
|
<th width="30%"><U><font size=+1>Field Name</font></U></th>
|
|
<th><U><font size=+1>Description</font></U></th>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Dimensionality</td>
|
|
<td>A chunk has a fixed dimensionality. This field
|
|
specifies the number of dimension size fields later in the
|
|
message.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Address</td>
|
|
<td>This is the address
|
|
of the B-tree that is used to look up the addresses of the
|
|
chunks.
|
|
The address
|
|
may have the "undefined address" value, to indicate that
|
|
storage has not yet been allocated for this array.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Dimensions</td>
|
|
<td>The dimension sizes define the size of a single chunk.</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<P>Class-specific information for compact layout (Class 2):
|
|
|
|
<p>
|
|
<center>
|
|
<table border cellpadding=4 width="80%">
|
|
<caption align=top>
|
|
<B>Property Descriptions</B>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=2>Size</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Raw Data</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>...</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<center>
|
|
<table align=center width="80%">
|
|
<tr align=left>
|
|
<th width="30%"><U><font size=+1>Field Name</font></U></th>
|
|
<th><U><font size=+1>Description</font></U></th>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Size</td>
|
|
<td>This field contains the size of the raw data for the dataset array.</td>
|
|
|
|
<tr valign=top>
|
|
<td>Raw Data</td>
|
|
<td>This field contains the raw data for the dataset array.</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
|
|
<hr>
|
|
<h4><a name="ReservedMessage_0009">Name: Reserved - Not Assigned Yet</a></h4>
|
|
<b>Header Message Type:</b> 0x0009<BR>
|
|
<b>Length:</b> N/A<BR>
|
|
<b>Status:</b> N/A<BR>
|
|
<b>Format of Data:</b> N/A<BR>
|
|
|
|
<p><b>Purpose and Description:</b> This message type was skipped during
|
|
the initial specification of the file format and may be used in a
|
|
future expansion to the format.
|
|
|
|
<hr>
|
|
<h4><a name="ReservedMessage_000A">Name: Reserved - Not Assigned Yet</a></h4>
|
|
<b>Header Message Type:</b> 0x000A<BR>
|
|
<b>Length:</b> N/A<BR>
|
|
<b>Status:</b> N/A<BR>
|
|
<b>Format of Data:</b> N/A<BR>
|
|
|
|
<p><b>Purpose and Description:</b> This message type was skipped during
|
|
the initial specification of the file format and may be used in a
|
|
future expansion to the format.
|
|
|
|
<hr>
|
|
<h4><a name="FilterMessage">Name: Data Storage - Filter Pipeline</a></h4>
|
|
<b>Header Message Type:</b> 0x000B<BR>
|
|
<b>Length:</b> varies<BR>
|
|
<b>Status:</b> Optional, may not be repeated.
|
|
|
|
<p><b>Purpose and Description:</b> This message describes the
|
|
filter pipeline which should be applied to the data stream by
|
|
providing filter identification numbers, flags, a name, an
|
|
client data.
|
|
|
|
<p>
|
|
<center>
|
|
<table border align=center cellpadding=4 width="80%">
|
|
<caption align=top>
|
|
<b>Filter Pipeline Message</b>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td>Version</td>
|
|
<td>Number of Filters</td>
|
|
<td colspan=2>Reserved</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Reserved</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4><br>Filter List<br><br></td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<center>
|
|
<table align=center width="80%">
|
|
<tr align=left>
|
|
<th width="30%"><U><font size=+1>Field Name</font></U></th>
|
|
<th><U><font size=+1>Description</font></U></th>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Version</td>
|
|
<td>The version number for this message. This document
|
|
describes version one.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Number of Filters</td>
|
|
<td>The total number of filters described by this
|
|
message. The maximum possible number of filters in a
|
|
message is 32.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Filter List</td>
|
|
<td>A description of each filter. A filter description
|
|
appears in the next table.</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<center>
|
|
<table border align=center cellpadding=4 width="80%">
|
|
<caption align=top>
|
|
<b>Filter Pipeline Message</b>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=2>Filter Identification</td>
|
|
<td colspan=2>Name Length</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=2>Flags</td>
|
|
<td colspan=2>Client Data Number of Values</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4><br>Name<br><br></td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4><br>Client Data<br><br></td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Padding</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<center>
|
|
<table align=center width="80%">
|
|
<tr align=left>
|
|
<th width="30%"><U><font size=+1>Field Name</font></U></th>
|
|
<th><U><font size=+1>Description</font></U></th>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Filter Identification</td>
|
|
<td>This is a unique (except in the case of testing)
|
|
identifier for the filter. Values from zero through 255
|
|
are reserved for filters defined by the NCSA HDF5
|
|
library. Values 256 through 511 have been set aside for
|
|
use when developing/testing new filters. The remaining
|
|
values are allocated to specific filters by contacting the
|
|
<a href="mailto:hdf5dev@ncsa.uiuc.edu">HDF5 Development
|
|
Team</a>.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Name Length</td>
|
|
<td>Each filter has an optional null-terminated ASCII name
|
|
and this field holds the length of the name including the
|
|
null termination padded with nulls to be a multiple of
|
|
eight. If the filter has no name then a value of zero is
|
|
stored in this field.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Flags</td>
|
|
<td>The flags indicate certain properties for a filter. The
|
|
bit values defined so far are:
|
|
|
|
<dl>
|
|
<dt><code>bit 1</code>
|
|
<dd>If set then the filter is an optional filter.
|
|
During output, if an optional filter fails it will be
|
|
silently removed from the pipeline.
|
|
</dl>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Client Data Number of Values</td>
|
|
<td>Each filter can store a few integer values to control
|
|
how the filter operates. The number of entries in the
|
|
Client Data array is stored in this field.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Name</td>
|
|
<td>If the Name Length field is non-zero then it will
|
|
contain the size of this field, a multiple of eight. This
|
|
field contains a null-terminated, ASCII character
|
|
string to serve as a comment/name for the filter.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Client Data</td>
|
|
<td>This is an array of four-byte integers which will be
|
|
passed to the filter function. The Client Data Number of
|
|
Values determines the number of elements in the
|
|
array.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Padding</td>
|
|
<td>Four bytes of zeros are added to the message at this
|
|
point if the Client Data Number of Values field contains
|
|
an odd number.</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<hr>
|
|
<h4><a name="AttributeMessage">Name: Attribute</a></h4>
|
|
<b>Header Message Type:</b> 0x000C<BR>
|
|
<b>Length:</b> varies<BR>
|
|
<b>Status:</b> Optional, may be repeated.<BR>
|
|
|
|
<p><b>Purpose and Description:</b> The <em>Attribute</em>
|
|
message is used to list objects in the HDF file which are used
|
|
as attributes, or "metadata" about the current object. An
|
|
attribute is a small dataset; it has a name, a datatype, a data
|
|
space, and raw data. Since attributes are stored in the object
|
|
header they must be relatively small (<64KB) and can be
|
|
associated with any type of object which has an object header
|
|
(groups, datasets, named types and spaces, etc.).
|
|
|
|
<p>Note: Attributes on an object must have unique names. (The HDF5 library
|
|
currently enforces this by causing the creation of an attribute with
|
|
a duplicate name to fail)
|
|
Attributes on different objects may have the same name, however.
|
|
|
|
<p>
|
|
<center>
|
|
<table border align=center cellpadding=4 width="80%">
|
|
<caption align=top>
|
|
<b>Attribute Message</b>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td>Version</td>
|
|
<td>Reserved</td>
|
|
<td colspan=2>Name Size</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=2>Type Size</td>
|
|
<td colspan=2>Space Size</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4><br>Name<br><br></td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4><br>Type<br><br></td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4><br>Space<br><br></td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4><br>Data<br><br></td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<center>
|
|
<table align=center width="80%">
|
|
<tr align=left>
|
|
<th width="30%"><U><font size=+1>Field Name</font></U></th>
|
|
<th><U><font size=+1>Description</font></U></th>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Version</td>
|
|
<td>Version number for the message. This document describes
|
|
version 1 of attribute messages.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Reserved</td>
|
|
<td>This field is reserved for later use and is set to
|
|
zero.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Name Size</td>
|
|
<td>The length of the attribute name in bytes including the
|
|
null terminator. Note that the Name field below may
|
|
contain additional padding not represented by this
|
|
field.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Type Size</td>
|
|
<td>The length of the datatype description in the Type
|
|
field below. Note that the Type field may contain
|
|
additional padding not represented by this field.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Space Size</td>
|
|
<td>The length of the dataspace description in the Space
|
|
field below. Note that the Space field may contain
|
|
additional padding not represented by this field.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Name</td>
|
|
<td>The null-terminated attribute name. This field is
|
|
padded with additional null characters to make it a
|
|
multiple of eight bytes.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Type</td>
|
|
<td>The datatype description follows the same format as
|
|
described for the datatype object header message. This
|
|
field is padded with additional zero bytes to make it a
|
|
multiple of eight bytes.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Space</td>
|
|
<td>The dataspace description follows the same format as
|
|
described for the dataspace object header message. This
|
|
field is padded with additional zero bytes to make it a
|
|
multiple of eight bytes.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Data</td>
|
|
<td>The raw data for the attribute. The size is determined
|
|
from the datatype and dataspace descriptions. This
|
|
field is <em>not</em> padded with additional zero
|
|
bytes.</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<hr>
|
|
<h4><a name="CommentMessage">Name: Object Comment</a></h4>
|
|
|
|
<p><b>Header Message Type:</b> 0x000D<br>
|
|
<b>Length:</b> varies<br>
|
|
<b>Status:</b> Optional, may not be repeated.
|
|
|
|
<p><b>Purpose and Description:</b> The object comment is
|
|
designed to be a short description of an object. An object comment
|
|
is a sequence of non-zero (<code>\0</code>) ASCII characters with no other
|
|
formatting included by the library.
|
|
|
|
<p>
|
|
<center>
|
|
<table border align=center cellpadding=4 width="80%">
|
|
<caption align=top>
|
|
<b>Name Message</b>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4><br>Comment<br><br></td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<center>
|
|
<table align=center width="80%">
|
|
<tr align=left>
|
|
<th width="30%"><U><font size=+1>Field Name</font></U></th>
|
|
<th><U><font size=+1>Description</font></U></th>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Name</td>
|
|
<td>A null terminated ASCII character string.</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<hr>
|
|
<h4><a name="OldModifiedMessage">Name: Object Modification Date & Time (Old)</a></h4>
|
|
|
|
<p><b>Header Message Type:</b> 0x000E<br>
|
|
<b>Length:</b> fixed<br>
|
|
<b>Status:</b> Optional, may not be repeated.
|
|
|
|
<p><b>Purpose and Description:</b> The object modification date
|
|
and time is a timestamp which indicates (using ISO-8601 date and
|
|
time format) the last modification of an object. The time is
|
|
updated when any object header message changes according to the
|
|
system clock where the change was posted.
|
|
|
|
<p>This modification time message is deprecated in favor of the "new"
|
|
modification time message (Message Type 0x0012) and is no longer written
|
|
to the file in versions of the HDF5 library after the 1.6.0 version.
|
|
</p>
|
|
|
|
|
|
<p>
|
|
<center>
|
|
<table border align=center cellpadding=4 width="80%">
|
|
<caption align=top>
|
|
<b>Modification Time Message</b>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Year</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=2>Month</td>
|
|
<td colspan=2>Day of Month</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=2>Hour</td>
|
|
<td colspan=2>Minute</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=2>Second</td>
|
|
<td colspan=2>Reserved</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<center>
|
|
<table align=center width="80%">
|
|
<tr align=left>
|
|
<th width="30%"><U><font size=+1>Field Name</font></U></th>
|
|
<th><U><font size=+1>Description</font></U></th>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Year</td>
|
|
<td>The four-digit year as an ASCII string. For example,
|
|
<code>1998</code>. All fields of this message should be interpreted
|
|
as coordinated universal time (UTC)</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Month</td>
|
|
<td>The month number as a two digit ASCII string where
|
|
January is <code>01</code> and December is <code>12</code>.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Day of Month</td>
|
|
<td>The day number within the month as a two digit ASCII
|
|
string. The first day of the month is <code>01</code>.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Hour</td>
|
|
<td>The hour of the day as a two digit ASCII string where
|
|
midnight is <code>00</code> and 11:00pm is <code>23</code>.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Minute</td>
|
|
<td>The minute of the hour as a two digit ASCII string where
|
|
the first minute of the hour is <code>00</code> and
|
|
the last is <code>59</code>.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Second</td>
|
|
<td>The second of the minute as a two digit ASCII string
|
|
where the first second of the minute is <code>00</code>
|
|
and the last is <code>59</code>.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Reserved</td>
|
|
<td>This field is reserved and should always be zero.</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<hr>
|
|
<h4><a name="SharedMessage">Name: Shared Object Message</a></h4>
|
|
<b>Header Message Type:</b> 0x000F<br>
|
|
<b>Length:</b> 4 Bytes<br>
|
|
<b>Status:</b> Optional, may be repeated.
|
|
|
|
<p>A constant message can be shared among several object headers
|
|
by writing that message in the global heap and having the object
|
|
headers all point to it. The pointing is accomplished with a
|
|
Shared Object message which is understood directly by the object
|
|
header layer of the library. It is also possible to have a
|
|
message of one object header point to a message in some other
|
|
object header, but care must be exercised to prevent cycles.
|
|
|
|
<p>If a message is shared, then the message appears in the global
|
|
heap and its message ID appears in the Header Message Type
|
|
field of the object header. Also, the Flags field in the object
|
|
header for that message will have bit two set (the
|
|
<code>H5O_FLAG_SHARED</code> bit). The message body in the
|
|
object header will be that of a Shared Object message defined
|
|
here and not that of the pointed-to message.
|
|
|
|
<p>
|
|
<center>
|
|
<table border cellpadding=4 width="80%">
|
|
<caption align=top>
|
|
<b>Shared Message Message</b>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</td>
|
|
<th width="25%">byte</td>
|
|
<th width="25%">byte</td>
|
|
<th width="25%">byte</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td>Version</td>
|
|
<td>Flags</td>
|
|
<td colspan=2>Reserved</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Reserved</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4><br>Pointer<br><br></td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<center>
|
|
<table align=center width="80%">
|
|
<tr align=left>
|
|
<th width="30%"><U><font size=+1>Field Name</font></U></th>
|
|
<th><U><font size=+1>Description</font></U></th>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Version</td>
|
|
<td>The version number for the message. This document
|
|
describes version one of shared messages.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Flags</td>
|
|
<td>The Shared Message message points to a message which is
|
|
shared among multiple object headers. The Flags field
|
|
describes the type of sharing:
|
|
|
|
<dl>
|
|
<dt><code>Bit 0</code>
|
|
<dd>If this bit is clear then the actual message is the
|
|
first message in some other object header; otherwise
|
|
the actual message is stored in the global heap.
|
|
|
|
<dt><code>Bits 2-7</code>
|
|
<dd>Reserved (always zero)
|
|
</dl>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Pointer</td>
|
|
<td>This field points to the actual message. The format of
|
|
the pointer depends on the value of the Flags field. If
|
|
the actual message is in the global heap then the pointer
|
|
is the file address of the global heap collection that
|
|
holds the message, and a four-byte index into that
|
|
collection. Otherwise the pointer is a group entry
|
|
that points to some other object header.</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
|
|
<hr>
|
|
<h4><a name="ContinuationMessage">Name: Object Header Continuation</a></h4>
|
|
<b>Header Message Type:</b> 0x0010<BR>
|
|
<b>Length:</b> fixed<BR>
|
|
<b>Status:</b> Optional, may be repeated.<BR>
|
|
<b>Purpose and Description:</b> The object header continuation is the location
|
|
in the file of more header messages for the current data object. This can be
|
|
used when header blocks are large, or likely to change over time.<BR>
|
|
<b>Format of Data:</b><p>
|
|
The object header continuation is formatted as follows (assuming a 4-byte
|
|
length & offset are being used in the current file):
|
|
|
|
<P>
|
|
<center>
|
|
<table border cellpadding=4 width=60%>
|
|
<caption align=bottom>
|
|
<B>HDF5 Object Header Continuation Message Layout</B>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width=25%>byte</th>
|
|
<th width=25%>byte</th>
|
|
<th width=25%>byte</th>
|
|
<th width=25%>byte</th>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Header Continuation Offset</td>
|
|
<tr align=center>
|
|
<td colspan=4>Header Continuation Length</td>
|
|
</table>
|
|
</center>
|
|
|
|
<P>
|
|
<dl>
|
|
<dt>The elements of the Header Continuation Message are described below:
|
|
<dd>
|
|
<dl>
|
|
<dt>Header Continuation Offset: (<offset> bytes)
|
|
<dd>This value is the offset in bytes from the beginning of the file where the
|
|
header continuation information is located.
|
|
<dt>Header Continuation Length: (<length> bytes)
|
|
<dd>This value is the length in bytes of the header continuation information in
|
|
the file.
|
|
</dl>
|
|
</dl>
|
|
|
|
<hr>
|
|
<h4><a name="SymbolTableMessage">Name: Group Message</a></h4>
|
|
<b>Header Message Type:</b> 0x0011<BR>
|
|
<b>Length:</b> fixed<BR>
|
|
<b>Status:</b> Required for groups, may not be repeated.<BR>
|
|
<b>Purpose and Description:</b> Each group has a B-tree and a
|
|
name heap which are pointed to by this message.<BR>
|
|
<b>Format of data:</b>
|
|
<p>The group message is formatted as follows:
|
|
|
|
<p>
|
|
<center>
|
|
<table border cellpadding=4 width="80%">
|
|
<caption align=bottom>
|
|
<b>HDF5 Object Header Group Message Layout</b>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>B-tree Address</td>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Heap Address</td>
|
|
</table>
|
|
</center>
|
|
|
|
<P>
|
|
<dl>
|
|
<dt>The elements of the Group Message are described below:
|
|
<dd>
|
|
<dl>
|
|
<dt>B-tree Address (<offset> bytes)
|
|
<dd>This value is the offset in bytes from the beginning of the file
|
|
where the B-tree is located.
|
|
<dt>Heap Address (<offset> bytes)
|
|
<dd>This value is the offset in bytes from the beginning of the file
|
|
where the group name heap is located.
|
|
</dl>
|
|
</dl>
|
|
|
|
<hr>
|
|
<h4><a name="ModifiedMessage">Name: Object Modification Date & Time</a></h4>
|
|
|
|
<P class=item><B>Header Message Type:</B> 0x0012
|
|
</P>
|
|
<P class=item><B>Length:</B> Fixed
|
|
</P>
|
|
<P class=item><B>Status:</B> Optional, may not be repeated.
|
|
</P>
|
|
|
|
<P class=item><B>Description:</B> The object modification date
|
|
and time is a timestamp which indicates
|
|
the last modification of an object. The time is
|
|
updated when any object header message changes according to the
|
|
system clock where the change was posted.
|
|
</P>
|
|
|
|
<p>
|
|
<center>
|
|
<table border align=center cellpadding=4 width="80%">
|
|
<caption align=top>
|
|
<b>Modification Time Message</b>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
<th width="25%">byte</th>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=1>Version</td>
|
|
<td colspan=3>Reserved</td>
|
|
</tr>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Seconds After Epoch</td>
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<center>
|
|
<table align=center width="80%">
|
|
<tr align=left>
|
|
<th width="30%"><U><font size=+1>Field Name</font></U></th>
|
|
<th><U><font size=+1>Description</font></U></th>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Version</td>
|
|
<td>The version number for the message. This document
|
|
describes version one of the new modification time message.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Reserved</td>
|
|
<td>This field is reserved and should always be zero.</td>
|
|
</tr>
|
|
|
|
<tr valign=top>
|
|
<td>Seconds After Epoch</td>
|
|
<td>The number of seconds since 0 hours, 0
|
|
minutes, 0 seconds, January 1, 1970, Coordinated Universal Time.
|
|
</tr>
|
|
</table>
|
|
</center>
|
|
|
|
<h3><a name="SharedObjectHeader">Disk Format: Level 2b - Shared Data Object Headers</a></h3>
|
|
<P>In order to share header messages between several dataset objects, object
|
|
header messages may be placed into the global heap. Since these
|
|
messages require additional information beyond the basic object header message
|
|
information, the format of the shared message is detailed below.
|
|
|
|
<BR> <BR>
|
|
<center>
|
|
<table border cellpadding=4 width=60%>
|
|
<caption align=bottom>
|
|
<B>HDF5 Shared Object Header Message</B>
|
|
</caption>
|
|
|
|
<tr align=center>
|
|
<th width=25%>byte</th>
|
|
<th width=25%>byte</th>
|
|
<th width=25%>byte</th>
|
|
<th width=25%>byte</th>
|
|
|
|
<tr align=center>
|
|
<td colspan=4>Reference Count of Shared Header Message</td>
|
|
<tr align=center>
|
|
<td colspan=4><br> Shared Object Header Message<br> <br></td>
|
|
</table>
|
|
</center>
|
|
|
|
<p>
|
|
<dl>
|
|
<dt> The elements of the shared object header message are described below:
|
|
<dd>
|
|
<dl>
|
|
<dt>Reference Count of Shared Header Message: (32-bit unsigned integer)
|
|
<dd>This value is used to keep a count of the number of dataset objects which
|
|
refer to this message from their dataset headers. When this count reaches zero,
|
|
the shared message header may be removed from the global heap.
|
|
<dt>Shared Object Header Message: (various lengths)
|
|
<dd>The data stored for the shared object header message is formatted in the
|
|
same way as the private object header messages described in the object header
|
|
description earlier in this document and begins with the header message Type.
|
|
</dl>
|
|
</dl>
|
|
|
|
|
|
<h3><a name="DataStorage">Disk Format: Level 2c - Data Object Data Storage</a></h3>
|
|
<P>The data for an object is stored separately from the header
|
|
information in the file and may not actually be located in the HDF5 file
|
|
itself if the header indicates that the data is stored externally. The
|
|
information for each record in the object is stored according to the
|
|
dimensionality of the object (indicated in the dimensionality header message).
|
|
Multi-dimensional data is stored in C order [same as current scheme], i.e. the
|
|
"last" dimension changes fastest.
|
|
<P>Data whose elements are composed of simple number-types are stored in
|
|
native-endian IEEE format, unless they are specifically defined as being stored
|
|
in a different machine format with the architecture-type information from the
|
|
number-type header message. This means that each architecture will need to
|
|
[potentially] byte-swap data values into the internal representation for that
|
|
particular machine.
|
|
<P> Data with a variable-length datatype is stored in the global heap
|
|
of the HDF5 file. Global heap identifiers are stored in the
|
|
data object storage.
|
|
<P>Data whose elements are composed of pointer number-types are stored in several
|
|
different ways depending on the particular pointer type involved. Simple
|
|
pointers are just stored as the dataset offset of the object being pointed to with the
|
|
size of the pointer being the same number of bytes as offsets in the file.
|
|
Dataset region references are stored as a heap-ID which points to the following
|
|
information within the file-heap: an offset of the object pointed to, number-type
|
|
information (same format as header message), dimensionality information (same
|
|
format as header message), sub-set start and end information (i.e. a coordinate
|
|
location for each), and field start and end names (i.e. a [pointer to the]
|
|
string indicating the first field included and a [pointer to the] string name
|
|
for the last field).
|
|
|
|
<P>Data of a compound datatype is stored as a contiguous stream of the items
|
|
in the structure, with each item formatted according to its datatype.</p>
|
|
|
|
<h3><a name="Appendix">Appendix</a></h3>
|
|
<P>Definitions of various terms used in this document.
|
|
</P>
|
|
<P>The <A name="UndefinedAddress">"undefined address"</A> for a file is a
|
|
file address with all bits set, i.e. <code>0xffff...ff</code>.
|
|
<P>The <A name="UnlimitedDim">"unlimited size"</A> for a size is a
|
|
value with all bits set, i.e. <code>0xffff...ff</code>.
|
|
|
|
<!-- #BeginLibraryItem "/ed_libs/NavBar_ADevG.lbi" --><hr>
|
|
<center>
|
|
<table border=0 width=98%>
|
|
<tr><td valign=top align=left>
|
|
<a href="index.html">HDF5 documents and links</a> <br>
|
|
<a href="H5.intro.html">Introduction to HDF5</a> <br>
|
|
<!--
|
|
<a href="Glossary.html">Glossary</a><br>
|
|
-->
|
|
</td>
|
|
<td valign=top align=right>
|
|
<a href="http://hdf.ncsa.uiuc.edu/HDF5/doc/UG/index.html">HDF5 User's Guide</a> <br>
|
|
<a href="RM_H5Front.html">HDF5 Reference Manual</a> <br>
|
|
<a href="ADGuide.html">HDF5 Application Developer's Guide</a> <br>
|
|
</td></tr>
|
|
</table>
|
|
</center>
|
|
<hr>
|
|
<!-- #EndLibraryItem --><!--
|
|
<address><a href="mailto:koziol@ncsa.uiuc.edu">Quincey Koziol</a></address>
|
|
<address><a href="mailto:matzke@llnl.gov">Robb Matzke</a></address>
|
|
-->
|
|
|
|
|
|
<!-- #BeginLibraryItem "/ed_libs/Footer.lbi" --><address>
|
|
<a href="mailto:hdfhelp@ncsa.uiuc.edu">HDF Help Desk</a>
|
|
<br>
|
|
Describes HDF5 Release 1.7, the unreleased development branch; working toward HDF5 Release 1.8.0
|
|
</address><!-- #EndLibraryItem --><!-- hhmts start -->
|
|
Last modified: 5 July 2002
|
|
<!-- hhmts end -->
|
|
|
|
</body>
|
|
</html>
|