openldap/doc/drafts/draft-good-ldap-changelog-xx.txt

Change Record Object Class Definition                       Gordon Good
INTERNET-DRAFT                                  Netscape Communications
                                                          10 March 2000

       Definition of an Object Class to Hold LDAP Change Records
               Filename: draft-good-ldap-changelog-01.txt

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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   This Internet Draft expires September 10, 2000.



Abstract

   In order to support more flexible replication methods, it is
   desirable to specify some manner in which an LDAP client may retrieve
   a set of changes which have been applied to an LDAP server's
   database.  The client, which may be another LDAP server, may then
   choose to update its own replicated copy of the data.  This document
   specifies an object class which may be used to represent changes
   applied to an LDAP server.  It also specifies a method for
   discovering the location of the container object which holds these
   change records, so that clients and servers have a common rendezvous
   point for this information.



Background and Intended Usage

   This document describes an objectclass which can be used to represent
   changes which have been applied to a directory server.  It also
   suggests a common location for a container which holds these objects.



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   A client may update its local copy of directory information by
   reading the entries within this container, and applying the changes
   to its local database.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", and "MAY" in this document are
   to be interpreted as described in RFC 2119 [3].

New Attribute Types Used in the changeLogEntry Object Class

   ( 2.16.840.1.113730.3.1.5
       NAME 'changeNumber'
       DESC 'a number which uniquely identifies a change made to a
             directory entry'
       SYNTAX 'INTEGER'
       EQUALITY 'integerMatch'
       ORDERING 'integerOrderingMatch' )

   ( 2.16.840.1.113730.3.1.6
       NAME 'targetDN'
       DESC 'the DN of the entry which was modified'
       EQUALITY distinguishedNameMatch
       SYNTAX 'DN' )

   ( 2.16.840.1.113730.3.1.7
       NAME 'changeType'
       DESC 'the type of change made to an entry'
       EQUALITY caseIgnoreMatch
       SYNTAX 'DirectoryString' )

   ( 2.16.840.1.113730.3.1.8
       NAME 'changes'
       DESC 'a set of changes to apply to an entry'
       SYNTAX 'OctetString' )

   ( 2.16.840.1.113730.3.1.9
       NAME 'newRDN'
       DESC 'the new RDN of an entry which is the target of a
             modrdn operation'
       EQUALITY distinguishedNameMatch
       SYNTAX 'DN' )

   ( 2.16.840.1.113730.3.1.10
       NAME 'deleteOldRDN'
       DESC 'a flag which indicates if the old RDN should be retained
             as an attribute of the entry'
       EQUALITY booleanMatch
       SYNTAX 'BOOLEAN' )



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   ( 2.16.840.1.113730.3.1.11
       NAME 'newSuperior'
       DESC 'the new parent of an entry which is the target of a
             moddn operation'
       EQUALITY distinguishedNameMatch
       SYNTAX 'DN' )


Schema Definition of the changeLogEntry Object Class

   ( 2.16.840.1.113730.3.2.1
       NAME 'changeLogEntry'
       SUP top
       STRUCTURAL
       MUST (
           changeNumber $ targetDN $ changeType
       )
       MAY (
           changes $ newRDN $ deleteOldRDN $ newSuperior
       )
   )



Discussion of changeLogEntry Attributes:

   changeNumber: the change number, as assigned by the supplier.  This
   integer MUST strictly increase as new entries are added, and must
   always be unique within a given server.  Syntax: INTEGER

   targetdn: the distinguished name of the entry which was added,
   modified or deleted.  In the case of a modrdn operation, the targetdn
   gives the DN of the entry before it was modified.  Syntax: DN

   changeType: the type of change. One of: "add", "delete", "modify",
   "modrdn".  Later RFCs may define additional values for changeType.
   Syntax: DirectoryString

   changes: the changes which were made to the directory server.  These
   changes are in LDIF format, which is described in [1].
   Syntax: OctetString

   newRDN: the new RDN (Relative Distinguished Name) of the entry, if the
   changeType is "modrdn".  If the changeType attribute does not have the
   value "modrdn", then there should be no values contained in the newRDN
   attribute.
   Syntax: DN




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   deleteOldRDN: a flag which tells whether the old RDN of the entry
   should be retained as a distinguished attribute of the entry, or
   should be deleted.  A value of "FALSE" indicates that the RDN should be
   retained as a distinguished attribute, and a value of "TRUE" indicates
   that it should not be retained as a distinguished attribute of the
   entry.  If any value other than "TRUE" or "FALSE" is contained in the
   deleteOldRDN attribute, or if the deleteOldRDN contains multiple
   values, the RDN should be retained as a distinguished attribute (that
   is, "FALSE" is the default if no values are present, or if illegal
   values are present).
   Syntax: BOOLEAN

   newSuperior: if present, gives the name of the entry which
   becomes the immediate superior of the existing entry.  This optional
   attribute reflects LDAPv3 functionality, and MUST NOT be generated
   by LDAPv2 servers [2].
   Syntax: DN



Discussion of the changeLogEntry object class

   The changeLogEntry object class is used to represent changes made to a
   directory server.  The set of changes made to a directory server, then,
   is given by the ordered set of all entries within the changelog
   container, ordered by changeNumber.

   A client may synchronize its local copy of a remote directory server's
   contents by searching the remote server's changelog container for any
   entries where the changenumber is greater than or equal to the last
   change previously retrieved from that server.  If the entry with the
   changenumber matching the last change retrieved is not returned in the
   search results, then the server's changelog has been trimmed.  The
   client must then fall back to reading the entire directory to bring its
   copy in sync with the server's.

   Assuming that the client has successfully retrieved one or more changelog
   entries from the server, it can then use the information contained in each
   entry to update the corresponding entry (named by the targetDN attribute)
   in its local copy of the database.

   Note that, due to access control restrictions, the client is not guaranteed
   read access to the "changes" attribute.  If the client discovers that the
   "changes" attribute has no values, then it must read the entry given by
   the targetDN attribute, possibly only retrieving attributes it deems
   "interesting".  However, in the case of delete and modrdn operations, there
   is never a "changes" attribute, so it is never necessary to read the target
   entry in these cases.



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Examples of the changeLogEntry object class

   In each example below, the "changes" attribute is shown in plain text,
   with embedded newlines.  This is done for clarity.  It is intended that
   newlines be stored in the entry literally, not encoded in any way.
   If a "changes" attribute value is stored in an LDIF file, it must
   base-64 encoded.

   Example 1: A changeLogEntry representing the addition of a
   new entry to the directory

   dn: changenumber=1923, cn=changelog
   changenumber: 1923
   targetdn: cn=Barbara Jensen, ou=Accounting, o=Ace Industry, c=US
   changetype: add
   changes: cn: Barbara Jensen\ncn: Babs Jensen\nsn: Jensen\n
    givenname: Barbara\ntelephonenumber: +1 212 555-1212\nmail: babs@ace.com\n
    objectclass: top\nobjectclass: person\nobjectclass: organizationalPerson\n
    objectclass: inetOrgPerson

   Example 2: A changeLogEntry representing the deletion of an entry
   from the directory

   dn: changenumber=2933, cn=changelog
   changenumber: 2933
   targetdn: cn=Gern Jensen, ou=Product Testing, o=Ace Industry, c=US
   changetype: delete

   Example 3: A changeLogEntry representing the modification of an entry
   in the directory

   dn: changenumber=5883, cn=changelog
   changenumber: 5883
   targetdn: cn=Bjorn Jensen, ou=Product Development, o=Ace Industry, c=US
   changetype: modify
   changes: delete: telephonenumber\ntelephonenumber: 1212\n-\n
    add: telephonenumber\ntelephonenumber: +1 212 555 1212\n-

   Example 4: A changeLogEntry representing a modrdn operation performed
   on an entry in the directory

   dn: changenumber=10042, cn=changelog
   changenumber: 10042
   targetdn: cn=Bjorn Jensen, ou=Product Development, o=Ace Industry, c=US
   changetype: modrdn
   newrdn: cn=Bjorn J Jensen
   deleteoldrdn: FALSE




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Location of the container containing changeLogEntry objects

   For LDAPv3 servers, the location of the container which holds
   changeLogEntry objects is obtained by reading the "changeLog" attribute
   of a server's root DSE.  For example, if the container's root is
   "cn=changelog", then the root DSE must have an attribute named
   "changeLog" with the value "cn=changelog".

   The "changelog" attribute is defined as follows:

   (   2.16.840.1.113730.3.1.35
       NAME 'changelog'
       DESC 'the distinguished name of the entry which contains
             the set of entries comprising this server's changelog'
       EQUALITY distinguishedNameMatch
       SYNTAX 'DN'
   )

   For LDAPv2 servers, the name of the changelog container must be
   "cn=changelog".

Interoperability between LDAPv2 and LDAPv3 implementations

   Implementors are discouraged from developing implementations in which
   an LDAPv2 server is synchronized from an LDAPv3 server using the
   changelog method described in this document. Problems can arise when an
   LDAPv2 server reads a "moddn" changelog entry which gives a new
   superior. Since LDAPv2 does not support such an operation, there is not
   way for the v2 server to perform the moddn operation atomically. It
   could, of course, delete all the entries under the old superior and add
   them under the new superior entry, but such an operation would either
   not be atomic, or require extensive server-side support on the LDAPv2
   server to make the operation appear as if it were atomic.

   It is recommended that servers which only implement LDAPv2 should
   refuse to synchronize from LDAPv3 servers. Before beginning
   synchronization, the LDAPv2 server should attempt to read the root DSE
   of the supplier server. If the root DSE is present, and the
   supportedldapversion attribute contained in the root DSE contains the
   value "3", then the LDAPv2 server should immediately disconnect and
   proceed no further with synchronization.

Security Considerations

   Servers implementing this scheme MUST NOT allow the "changes"
   attribute to be generally readable.  The "changes" attribute contains
   all modifications made to an entry, and some changes may contain
   sensitive data, e.g. passwords.



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   If a server does allow read access on the "changes: attribute to a
   particular bound DN, then that DN should be trusted.  For example, two
   cooperating servers may exchange the password for some DN which is
   granted read access to the "changes" attribute of the changeLog.  This
   would allow one server to retrieve changes and apply them directly to
   its database.

   In situations where the "changes" attribute is not readable by a client,
   that client may still use the entries in the changeLog to construct a
   list of entry DNs which are known to have changed since the last time
   the client synchronized.  The client may then read each of those entries,
   subject to whatever access control is in effect on the server,
   and update its local copy of each entry.

   Servers implementing this scheme should disallow write access to the
   changelog container object and all entries contained within.



Acknowledgements

   This material is based in part upon work supported by the National
   Science Foundation under Grant No. NCR-9416667.



References

   [1] Good, G., "The LDAP Data Interchange Format", INTERNET-DRAFT
   draft-good-ldap-ldif-06.txt, Netscape Communications Corp., March 2000
   <URL:ftp://ftp.ietf.org/internet-drafts/draft-good-ldap-ldif-06.txt>

   [2] Wahl, M., Howes, T., Kille, S., "Lightweight Directory Access
   Protocol (v3)", RFC 2251 Critical Angle, Inc., Netscape Communications Corp.,
   ISODE Consortium, July, 1997,
   <URL:ftp://ftp.isi.edu/in-notes/rfc2251.txt>

   [3] S. Bradner, "Key Words for use in RFCs to Indicate Requirement
   Levels", Harvard University, RFC 2119, March 1997,
   <URL:http://ds.internic.net/rfc/rfc2119.txt>


Author's Address

   Gordon Good
   Netscape Communications Corp.
   501 E. Middlefield Rd.
   Mailstop MV068



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   Mountain View, CA 94043, USA
   Phone:  +1 650 937-3825
   EMail:  ggood@netscape.com

              This Internet Draft expires September 10, 2000














































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