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<h1>DDL in BNF for HDF5</h1>


<h2>1. Introduction</h2>

This document contains the data description language (DDL) for an HDF5 file. 
The description is in Backus-Naur Form.  

<h2>2. Explanation of Symbols</h2>

This section contains a brief explanation of the symbols used in the DDL.

<PRE>
    ::=                      defined as
    &lt;tname&gt;                  a token with the name tname
    &lt;a&gt; | &lt;b&gt;                one of &lt;a&gt; or &lt;b&gt;
    &lt;a&gt;<FONT SIZE=1.7>opt</FONT>                    zero or one occurrence of &lt;a&gt;
    &lt;a&gt;*                     zero or more occurrence of &lt;a&gt;
    &lt;a&gt;+                     one or more occurrence of &lt;a&gt;
    TBD                      To Be Decided
</pre>

<h2>3. The DDL</h2>

<dir>
<pre>
&lt;file&gt; ::= HDF5 &lt;file_name&gt; { &lt;file_super_block&gt;<FONT SIZE=1.7>opt</FONT> &lt;root_group&gt; }

&lt;file_name&gt; ::= &lt;identifier&gt;

&lt;file_super_block&gt; ::= BOOT_BLOCK { &lt;super_block_content&gt; }

&lt;super_block_content&gt; ::= TBD

&lt;root_group&gt; ::= GROUP "/" { &lt;unamed_datatype&gt;* &lt;object_id&gt;<FONT SIZE=1.7>opt</FONT>
            &lt;group_attribute&gt;* &lt;group_member&gt;* }  

&lt;datatype&gt; ::= &lt;atomic_type&gt | &lt;compound_type&gt | &lt;variable_length_type&gt |
            &lt;array_type&gt

&lt;unamed_datatype&gt; ::= DATATYPE &lt;unamed_type_name&gt; { &lt;datatype&gt; }

&lt;unamed_type_name&gt; ::= the assigned name for unamed type is in the form of 
           #oid1:oid2, where oid1 and oid2 are the object ids of the type

&lt;atomic_type&gt; ::= &lt;integer&gt; | &lt;float&gt; | &lt;time&gt; | &lt;string&gt; | &lt;bitfield&gt; |
               &lt;opaque&gt; | &lt;reference&gt; | &lt;enum&gt;

&lt;integer&gt; ::=  H5T_STD_I8BE | H5T_STD_I8LE | H5T_STD_I16BE |
           H5T_STD_I16LE | H5T_STD_I32BE | H5T_STD_I32LE | H5T_STD_I64BE |
           H5T_STD_I64LE | H5T_STD_U8BE | H5T_STD_U8LE | H5T_STD_U16BE |
           H5T_STD_U16LE | H5T_STD_U32BE | H5T_STD_U32LE | H5T_STD_U64BE |
           H5T_STD_U64LE | H5T_NATIVE_CHAR | H5T_NATIVE_UCHAR |
           H5T_NATIVE_SHORT | H5T_NATIVE_USHORT | H5T_NATIVE_INT |
           H5T_NATIVE_UINT | H5T_NATIVE_LONG | H5T_NATIVE_ULONG |
           H5T_NATIVE_LLONG | H5T_NATIVE_ULLONG

&lt;float&gt; ::= H5T_IEEE_F32BE | H5T_IEEE_F32LE | H5T_IEEE_F64BE |
            H5T_IEEE_F64LE | H5T_NATIVE_FLOAT |  H5T_NATIVE_DOUBLE |
            H5T_NATIVE_LDOUBLE

&lt;time&gt; ::= TBD

&lt;string&gt; ::= H5T_STRING { STRSIZE &lt;strsize&gt; ;
               STRPAD &lt;strpad&gt; ;
               CSET &lt;cset&gt; ;
               CTYPE &lt;ctype&gt; ; }  

&lt;strsize&gt; ::= an integer

&lt;strpad&gt; ::= H5T_STR_NULLTERM | H5T_STR_NULLPAD | H5T_STR_SPACEPAD

&lt;cset&gt; ::= H5T_CSET_ASCII

&lt;ctype&gt; ::= H5T_C_S1 | H5T_FORTRAN_S1

&lt;bitfield&gt; ::= TBD

&lt;opaque&gt; ::= H5T_OPAQUE { &lt;identifier&gt; }

&lt;reference&gt; ::= H5T_REFERENCE { &lt;ref_type&gt; }

&lt;ref_type&gt; ::= H5T_STD_REF_OBJECT | H5T_STD_REF_DSETREG

&lt;compound_type&gt; ::= H5T_COMPOUND { &lt;member_type_def&gt;+ }

&lt;member_type_def&gt; ::= &lt;datatype&gt; &lt;field_name&gt; ;

&lt;field_name&gt; ::= &lt;identifier&gt;

&lt;variable_length_type&gt; ::= H5T_VLEN { &lt;datatype&gt }

&lt;array_type&gt; ::= H5T_ARRAY { &lt;dim_sizes&gt; &lt;datatype&gt; }

&lt;dim_sizes&gt; ::= [dimsize1][dimsize2]...
// where dimsize1, dimsize2 are integers

&lt;attribute&gt; ::= ATTRIBUTE &lt;attr_name&gt; { &lt;dataset_type&gt;    
                                        &lt;dataset_space&gt;
                                        &lt;data&gt;<FONT SIZE=1.7>opt</FONT>  } 

&lt;attr_name&gt; ::= &lt;identifier&gt;

&lt;dataset_type&gt; ::= DATATYPE &lt;path_name&gt; | &lt;datatype&gt;

&lt;enum&gt; ::= H5T_ENUM { &lt;enum_base_type&gt; &lt;enum_def&gt;+  }

&lt;enum_base_type&gt; ::= &lt;integer&gt;
// Currently enums can only hold integer type data, but they may be expanded
// in the future to hold any datatype

&lt;enum_def&gt; ::= &lt;enum_symbol&gt; &lt;enum_val&gt;;

&lt;enum_symbol&gt; ::= &lt;identifier&gt;

&lt;enum_val&gt; ::= an integer;

&lt;path_name&gt; ::= &lt;path_part&gt;+

&lt;path_part&gt; ::= /&lt;identifier&gt;

&lt;dataspace&gt; ::= &lt;scalar_space&gt | &lt;simple_space&gt | &lt;complex_space&gt

&lt;scalar_space&gt; ::= SCALAR

&lt;simple_space&gt; ::= SIMPLE { &lt;current_dims&gt; / &lt;max_dims&gt; }

&lt;complex_space&gt; ::= COMPLEX { &lt;complex_space_definition&gt; }

&lt;dataset_space&gt; ::= DATASPACE &lt;path_name&gt; | &lt;dataspace&gt;

&lt;current_dims&gt; ::= (<i>i<FONT SIZE=1.0>1</i></FONT>, <i>i<FONT SIZE=1.0>2</i></FONT>, ... ), where <i>i<FONT SIZE=1.0>k</i></FONT> is an integer, <i>k</i> = 1,2,...

&lt;max_dims&gt; ::= (<i>i<FONT SIZE=1.0>1</i></FONT>, <i>i<FONT SIZE=1.0>2</i></FONT>, ... ) where <i>i<FONT SIZE=1.0>k</i></FONT> is an integer or H5S_UNLIMITED

&lt;complex_space_definition&gt; ::= TBD

&lt;data&gt; ::= DATA { &lt;scalar_space_data&gt; | &lt;simple_space_data&gt; |
              &lt;complex_space_data&gt; }
                  
&lt;scalar_space_data&gt; ::= &lt;any_element&gt;

&lt;any_element&gt; ::= &lt;atomic_element&gt; | &lt;compound_element&gt; | 
        &lt;variable_length_element&gt; | &lt;array_element&gt;

&lt;any_data_seq&gt; ::= &lt;any_element&gt; | &lt;any_element&gt;, &lt;any_data_seq&gt;

&lt;atomic_element&gt; :: = &lt;integer_data&gt; | &lt;float_data&gt; | &lt;time_data&gt; |
                &lt;string_data&gt; | &lt;bitfield_data&gt; | &lt;opaque_data&gt; |
                &lt;enum_data&gt; | &lt;reference_data&gt;

&lt;integer_data&gt; ::= an integer

&lt;float_data&gt; ::= a floating point number

&lt;time_data&gt; ::= TBD

&lt;string_data&gt; ::= a string
// A string is enclosed in double quotes. 
// If a string is displayed on more than one line, string concatenate
// operator '//'is used.

&lt;bitfield_data&gt; ::= TBD

&lt;opaque_data&gt; ::= TBD

&lt;enum_data&gt; ::= &lt;enum_symbol&gt;

&lt;reference_data&gt; ::= &lt;object_ref_data&gt; | &lt;data_region_data&gt; | NULL

&lt;object_ref_data&gt; ::= &lt;object_type&gt; &lt;object_num&gt;

&lt;object_type&gt; ::= DATASET | GROUP | DATATYPE

&lt;object_id&gt; ::= OBJECTID { &lt;object_num&gt; }

&lt;object_num&gt; ::= an integer:an integer | an integer

&lt;data_region_data&gt; ::= H5T_STD_REF_DSETREG &lt;object_num&gt;
        { &lt;data_region_data_info&gt;, &lt;data_region_data_info&gt;, ...}

&lt;data_region_data_info&gt; ::= &lt;region_info&gt; | &lt;point_info&gt;

&lt;region_info&gt; ::= (&lt;lower_bound&gt;:&lt;upper_bound&gt;,
        &lt;lower_bound&gt;:&lt;upper_bound&gt;, ...)

&lt;lower_bound&gt; ::= an integer

&lt;upper_bound&gt; ::= an integer

&lt;point_info&gt; ::= (an integer, an integer, ...)

&lt;compound_element&gt; ::= { &lt;any_data_seq&gt; }

&lt;atomic_simple_data&gt; :: = &lt;atomic_element&gt;, &lt;atomic_simple_data&gt; |
        &lt;atomic_element&gt;

&lt;simple_space_data&gt; :: = &lt;any_data_seq&gt;

&lt;variable_length_element&gt; ::= ( &lt;any_data_seq&gt; )

&lt;array_element&gt; ::= [ &lt;any_data_seq&gt; ]

&lt;complex_space_data&gt; ::= TBD

&lt;named_datatype&gt; ::= DATATYPE &lt;type_name&gt; { &lt;datatype&gt; }

&lt;type_name&gt; ::= &lt;identifier&gt;

&lt;named_dataspace&gt; ::= TBD

&lt;hardlink&gt; ::= HARDLINK &lt;path_name&gt; 

&lt;group&gt; ::= GROUP &lt;group_name&gt; { &lt;hardlink&gt; | &lt;group_info&gt; }
            
&lt;group_name&gt; ::= &lt;identifier&gt;

&lt;group_info&gt; ::= &lt;group_attribute&gt;* &lt;group_member&gt;* 
            
&lt;group_attribute&gt; ::= &lt;attribute&gt; 

&lt;group_member&gt; ::= &lt;named_datatype&gt; | &lt;named_dataspace&gt; | &lt;group&gt; |
        &lt;dataset&gt; | &lt;softlink&gt;

&lt;dataset&gt; ::= DATASET &lt;dataset_name&gt; { &lt;hardlink&gt; | &lt;dataset_info&gt; }

&lt;dataset_info&gt; ::= &lt;dataset_type&gt;  &lt;dataset_space&gt; &lt;storagelayout&gt;<FONT SIZE=1.7>opt</FONT>
               &lt;compression&gt;<FONT SIZE=1.7>opt</FONT> &lt;dataset_attribute&gt;* &lt;object_id&gt;<FONT SIZE=1.7>opt</FONT>
               &lt;data&gt;<FONT SIZE=1.7>opt</FONT>
// Tokens above can be in any order as long as &lt;data&gt; is 
// after &lt;dataset_type&gt; and &lt;dataset_space&gt;.

&lt;dataset_name&gt; ::= &lt;identifier&gt;

&lt;storagelayout&gt; :: = STORAGELAYOUT &lt;contiguous_layout&gt;  |  
                     STORAGELAYOUT &lt;chunked_layout&gt;  | 
                     STORAGELAYOUT &lt;compact_layout&gt;  | 
                     STORAGELAYOUT &lt;external_layout&gt; 

&lt;contiguous_layout&gt; ::= {CONTIGUOUS}    // default

&lt;chunked_layout&gt; ::=  {CHUNKED &lt;dims&gt; }

&lt;dims&gt; ::= (<i>i<FONT SIZE=1.0>1</i></FONT>, <i>i<FONT SIZE=1.0>2</i></FONT>, ... ), <i>i<FONT SIZE=1.0>k</i></FONT> is an integer, <i>k</i> = 1,2,... 

&lt;compact_layout&gt; ::= TBD           

&lt;external_layout&gt; ::= {EXTERNAL &lt;external_file&gt;+ }

&lt;external_file&gt; ::= (&lt;file_name&gt; &lt;offset&gt; &lt;size&gt;) 

&lt;offset&gt; ::= an integer

&lt;size&gt; ::= an integer

&lt;compression&gt; :: = COMPRESSION { TBD }  

&lt;dataset_attribute&gt; ::= &lt;attribute&gt; 

&lt;softlink&gt; ::= SOFTLINK &lt;softlink_name&gt; { LINKTARGET &lt;target&gt; }

&lt;softlink_name&gt; ::= &lt;identifier&gt;

&lt;target&gt; ::= &lt;identifier&gt;

&lt;identifier&gt; ::= string   
// character '/' should be used with care. 

</PRE>
</dir>


<h2>4. An Example of an HDF5 File in DDL</h2>

<dir>
<PRE>
HDF5 "example.h5" {
GROUP "/" {
   ATTRIBUTE "attr1" {
      DATATYPE H5T_STRING { 
           STRSIZE 17;
           STRPAD H5T_STR_NULLTERM;
           CSET H5T_CSET_ASCII;
           CTYPE H5T_C_S1;
         }
      DATASPACE SCALAR 
      DATA {
         "string attribute"
      }
   }
   DATASET "dset1" {
      DATATYPE H5T_STD_I32BE
      DATASPACE SIMPLE { ( 10, 10 ) / ( 10, 10 ) }
      DATA {
         0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
         0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
         0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
         0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
         0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
         0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
         0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
         0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
         0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
         0, 1, 2, 3, 4, 5, 6, 7, 8, 9
      }
   }
   DATASET "dset2" {
      DATATYPE H5T_COMPOUND {
         H5T_STD_I32BE "a";
         H5T_IEEE_F32BE "b";
         H5T_IEEE_F64BE "c";
      }
      DATASPACE SIMPLE { ( 5 ) / ( 5 ) }
      DATA {
         {
            1,
            0.1,
            0.01
         },
         {
            2,
            0.2,
            0.02
         },
         {
            3,
            0.3,
            0.03
         },
         {
            4,
            0.4,
            0.04
         },
         {
            5,
            0.5,
            0.05
         }
      }
   }
   GROUP "group1" {
      DATASET "dset3" {
         DATATYPE "/type1"
         DATASPACE SIMPLE { ( 5 ) / ( 5 ) }
         DATA {
            {
               [ 0, 1, 2, 3 ],
               [ 0.1, 0.1, 0.1, 0.1, 0.1, 0.1,
                 0.2, 0.2, 0.2, 0.2, 0.2, 0.2,
                 0.3, 0.3, 0.3, 0.3, 0.3, 0.3,
                 0.4, 0.4, 0.4, 0.4, 0.4, 0.4,
                 0.5, 0.5, 0.5, 0.5, 0.5, 0.5 ]
            },
            {
               [ 0, 1, 2, 3 ],
               [ 0.1, 0.1, 0.1, 0.1, 0.1, 0.1,
                 0.2, 0.2, 0.2, 0.2, 0.2, 0.2,
                 0.3, 0.3, 0.3, 0.3, 0.3, 0.3,
                 0.4, 0.4, 0.4, 0.4, 0.4, 0.4,
                 0.5, 0.5, 0.5, 0.5, 0.5, 0.5 ]
            },
            {
               [ 0, 1, 2, 3 ],
               [ 0.1, 0.1, 0.1, 0.1, 0.1, 0.1,
                 0.2, 0.2, 0.2, 0.2, 0.2, 0.2,
                 0.3, 0.3, 0.3, 0.3, 0.3, 0.3,
                 0.4, 0.4, 0.4, 0.4, 0.4, 0.4,
                 0.5, 0.5, 0.5, 0.5, 0.5, 0.5 ]
            },
            {
               [ 0, 1, 2, 3 ],
               [ 0.1, 0.1, 0.1, 0.1, 0.1, 0.1,
                 0.2, 0.2, 0.2, 0.2, 0.2, 0.2,
                 0.3, 0.3, 0.3, 0.3, 0.3, 0.3,
                 0.4, 0.4, 0.4, 0.4, 0.4, 0.4,
                 0.5, 0.5, 0.5, 0.5, 0.5, 0.5 ]
            },
            {
               [ 0, 1, 2, 3 ],
               [ 0.1, 0.1, 0.1, 0.1, 0.1, 0.1,
                 0.2, 0.2, 0.2, 0.2, 0.2, 0.2,
                 0.3, 0.3, 0.3, 0.3, 0.3, 0.3,
                 0.4, 0.4, 0.4, 0.4, 0.4, 0.4,
                 0.5, 0.5, 0.5, 0.5, 0.5, 0.5 ]
            }
         }
      }
   }
   DATASET "dset3" {
      DATATYPE H5T_VLEN { H5T_STD_I32LE } 
      DATASPACE SIMPLE { ( 4 ) / ( 4 ) } 
      DATA {
         (0), (10, 11), (20, 21, 22), (30, 31, 32, 33)
      } 
   }
   GROUP "group2" {
      HARDLINK "/group1"
   }
   SOFTLINK "slink1" {
      LINKTARGET "somevalue"
   }
   DATATYPE "type1" H5T_COMPOUND {
      H5T_ARRAY { [4] H5T_STD_I32BE } "a";
      H5T_ARRAY { [5][6] H5T_IEEE_F32BE } "b";
   }
}
}
</pre>
</dir>


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      DDL&nbsp;&nbsp;
      <br>
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<hr>
<address>
<a href="mailto:hdfhelp@ncsa.uiuc.edu">HDF Help Desk</a>
</address>

Last modified:  17 November 2000

<br>
Describes HDF5 Release 1.4 Beta, December 2000


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