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Network Working Group                                             H. Chu
Internet-Draft                                               Symas Corp.
Intended status: Informational                                  May 2006
Expires: November 2, 2006


                   Ordered Entries and Values in LDAP
                     draft-chu-ldap-xordered-00.txt

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Copyright Notice

   Copyright (C) The Internet Society (2006).


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Abstract

   As LDAP is used more extensively for managing various kinds of data,
   one often encounters a need to preserve both the ordering and the
   content of data, despite the inherently unordered structure of
   entries and attribute values in the directory.  This document
   describes a scheme to attach ordering information to attributes in a
   directory so that the ordering may be preserved and propagated to
   other LDAP applications.


Table of Contents

   1.          Introduction . . . . . . . . . . . . . . . . . . . . .  3
   2.          Conventions  . . . . . . . . . . . . . . . . . . . . .  4
   3.          Ordering Extension . . . . . . . . . . . . . . . . . .  5
   3.1.        Overview . . . . . . . . . . . . . . . . . . . . . . .  5
   3.2.        Encoding . . . . . . . . . . . . . . . . . . . . . . .  5
   3.3.        Ordering Properties  . . . . . . . . . . . . . . . . .  6
   4.          Examples . . . . . . . . . . . . . . . . . . . . . . .  8
   4.1.        Sample Schema  . . . . . . . . . . . . . . . . . . . .  8
   4.2.        Ordered Values . . . . . . . . . . . . . . . . . . . .  8
   4.3.        Ordered Siblings . . . . . . . . . . . . . . . . . . . 10
   5.          Security Considerations  . . . . . . . . . . . . . . . 13
   6.          Normative References . . . . . . . . . . . . . . . . . 14
   Appendix A. IANA Considerations  . . . . . . . . . . . . . . . . . 15
               Author's Address . . . . . . . . . . . . . . . . . . . 16
               Intellectual Property and Copyright Statements . . . . 17


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1.  Introduction

   Information in LDAP directories is usually handled by applications in
   the form of ordered lists, which tends to encourage application
   developers to assume they are maintained as such, i.e., it is assumed
   that information stored in a particular order will always be
   retrieved and presented in that same order.  The fact that directory
   attributes actually store sets of values, which are inherently
   unordered, often causes grief to users migrating their data into
   LDAP.  Similar concerns arise over the order in which entries
   themselves are stored and retrieved from the directory.

   This document describes a schema extension that may be used in LDAP
   attribute definitions to store ordering information along with the
   attribute values, so that the ordering can be recovered when
   retrieved by an LDAP client.  The extension also provides automated
   management of this ordering information to ease manipulation of the
   ordered values.


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2.  Conventions

   Imperative keywords defined in [RFC2119] are used in this document,
   and carry the meanings described there.


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3.  Ordering Extension

3.1.  Overview

   The &quot;X-ORDERED&quot; schema extension is added to an
   AttributeTypeDescription to signify the use of this ordering
   mechanism.  The extension has two variants, selected by either the
   'VALUES' or 'SIBLINGS' qdstrings.  In general this extension is only
   compatible with AttributeTypes that have a string-oriented syntax.

   The &quot;X-ORDERED 'VALUES'&quot; extension is used with multi-valued
   attributes to maintain the order of multiple values of a given
   attribute.  For example, this feature is useful for storing data such
   as access control rules, which must be evaluated in a specific order.
   If the access control information is stored in a multi-valued
   attribute without a means of preserving the the order of the rules,
   the access control rules cannot be evaluated properly.  As the use of
   LDAP to store security policy and access control information becomes
   more prevalent, the necessity of this feature continues to grow.

   The &quot;X-ORDERED 'SIBLINGS'&quot; extension is used with single-valued
   attributes to maintain the order of all the onelevel children of a
   parent entry.  That is, ordering will be maintained for all the child
   entries whose RDNs are all of the same AttributeType.  The motivation
   for this feature is much the same as for the 'VALUES' feature.
   Sometimes the information with the ordering dependency is too complex
   or highly structured to be conveniently stored in values of a multi-
   valued attribute.  For example, one could store a prioritized list of
   servers as a set of separate entries, each entry containing separate
   attributes for a URL, a set of authentication credentials, and
   various other parameters.  Using the 'SIBLINGS' feature with the
   attribute in the entries' RDNs would ensure that when obtaining the
   list of these entries, the list is returned in the intended order.

3.2.  Encoding

   Ordering information is encoded by prepending a value's ordinal index
   to each value, enclosed in braces.  The following BNF specifies the
   encoding.  It uses elements defined in [RFC2252].

      d = &quot;0&quot; / &quot;1&quot; / &quot;2&quot; / &quot;3&quot; / &quot;4&quot; / &quot;5&quot; / &quot;6&quot; / &quot;7&quot; / &quot;8&quot; / &quot;9&quot;

      numericstring = 1*d

      ordering-prefix = &quot;{&quot; numericstring &quot;}&quot;

      value = &lt;any sequence of octets&gt;


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      ordered-value = ordering-prefix value

   The ordinals are zero-based and increment by one for each value.

   Note that when storing ordered-values into the directory, the
   ordering-prefix can usually be omitted as it will be generated
   automatically.  But if the original value already begins with a
   sequence of characters in the form of an ordering-prefix, then an
   ordering-prefix must always be provided with that value, otherwise
   the value will be processed and stored incorrectly.

   Using this extension on an attribute requires that ordering-prefix is
   a legal value of the LDAP syntax of that attribute.

3.3.  Ordering Properties

   Since the ordering-prefix is stored with the attribute values, it
   will be propagated to any clients or servers that access the data.

   Servers implementing this scheme SHOULD sort the values according to
   their ordering-prefix before returning them in search results.

   The presence of the ordering extension alters the matching rules that
   apply to the attribute:

      When presented with an AssertionValue that does not have an
      ordering-prefix, the ordering-prefix in the AttributeValue is
      ignored.

      When presented with an AssertionValue that consists solely of an
      ordering-prefix, only the ordering-prefix of the AttributeValue is
      compared; the remainder of the value is ignored.

      When presented with an AssertionValue containing both the
      ordering-prefix and a value, both components are compared to
      determine a match.

   A side effect of these properties is that even attributes that
   normally would have no equality matching rule can be matched by an
   ordering-prefix.

   The ordering-prefix may also be used in Modification requests to
   specify which values to delete, and in which position values should
   be added.  When processing deletions and insertions, all of the
   ordinals are recounted after each individual modification.

   If a value being added does not have an ordering-prefix, it is simply
   appended to the list and the appropriate ordering-prefix is


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   automatically generated.  Likewise if an ordering-prefix is provided
   that is greater than or equal to the number of existing values.

   See the examples in the next section.


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4.  Examples

4.1.  Sample Schema

   This schema is used for all of the examples:

   ( EXAMPLE_AT.1 NAME 'olcDatabase'
   EQUALITY caseIgnoreMatch
   SYNTAX 1.3.6.1.4.1.1466.115.121.1.15
   SINGLE-VALUE X-ORDERED 'SIBLINGS' )

   ( EXAMPLE_AT.2 NAME 'olcSuffix'
   EQUALITY distinguishedNameMatch
   SYNTAX 1.3.6.1.4.1.1466.115.121.1.12
   X-ORDERED 'VALUES' )

   ( EXAMPLE_OC.1 NAME 'olcDatabaseConfig'
   SUP top STRUCTURAL
   MAY ( olcDatabase $ olcSuffix ) )

4.2.  Ordered Values

   Given this entry:

   dn: olcDatabase={1}bdb,cn=config
   olcDatabase: {1}bdb
   objectClass: olcDatabaseConfig
   olcSuffix: {0}dc=example,dc=com
   olcSuffix: {1}o=example.com
   olcSuffix: {2}o=The Example Company
   olcSuffix: {3}o=example,c=us

   We can perform these Modify operations:

   1.  dn: olcDatabase={1}bdb,cn=config
       changetype: modify
       delete: olcSuffix
       olcSuffix: {0}
       -
       This operation deletes the first olcSuffix, regardless of its
       value.  All other values are bumped up one position.  The
       olcSuffix attribute will end up containing:
       olcSuffix: {0}o=example.com
       olcSuffix: {1}o=The Example Company
       olcSuffix: {2}o=example,c=us

   2.  Starting from the original entry, we could issue this change
       instead:


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       delete: olcSuffix
       olcSuffix: o=example.com
       -
       This operation deletes the olcSuffix that matches the value,
       regardless of its ordering-prefix.  The olcSuffix attribute will
       contain:
       olcSuffix: {0}dc=example,dc=com
       olcSuffix: {1}o=The Example Company
       olcSuffix: {2}o=example,c=us

   3.  Again, starting from the original entry, we could issue this
       change:
       delete: olcSuffix
       olcSuffix: {2}o=The Example Company
       -
       Here both the ordering-prefix and the value must match, otherwise
       the Modify would fail with noSuchAttribute.  In this case the
       olcSuffix attribute results in:
       olcSuffix: {0}dc=example,dc=com
       olcSuffix: {1}o=example.com
       olcSuffix: {2}o=example,c=us

   4.  Adding a new value without an ordering-prefix simply appends:
       add: olcSuffix
       olcSuffix: o=example.org
       -
       The resulting attribute would be:
       olcSuffix: {0}dc=example,dc=com
       olcSuffix: {1}o=example.com
       olcSuffix: {2}o=The Example Company
       olcSuffix: {3}o=example,c=us
       olcSuffix: {4}o=example.org

   5.  Adding a new value with an ordering-prefix inserts into the
       specified position:
       add: olcSuffix
       olcSuffix: {0}o=example.org
       -
       The resulting attribute would be:
       olcSuffix: {0}o=example.org
       olcSuffix: {1}dc=example,dc=com
       olcSuffix: {2}o=example.com
       olcSuffix: {3}o=The Example Company
       olcSuffix: {4}o=example,c=us

   6.  Modifying multiple values in one operation:
       add: olcSuffix
       olcSuffix: {0}ou=Dis,o=example.com


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       olcSuffix: {0}ou=Dat,o=example,com
       -
       delete: olcSuffix:
       olcSuffix: {2}
       olcSuffix: {1}
       -
       The resulting attribute would be:
       olcSuffix: {0}ou=Dat,o=example,com
       olcSuffix: {1}dc=example,dc=com
       olcSuffix: {2}o=example.com
       olcSuffix: {3}o=The Example Company
       olcSuffix: {4}o=example,c=us

   7.  If the Adds and Deletes in the previous example were done in the
       opposite order:
       delete: olcSuffix:
       olcSuffix: {2}
       olcSuffix: {1}
       -
       add: olcSuffix
       olcSuffix: {0}ou=Dis,o=example.com
       olcSuffix: {0}ou=Dat,o=example,com
       -
       The result would be:
       olcSuffix: {0}ou=Dat,o=example,com
       olcSuffix: {1}ou=Dis,o=example.com
       olcSuffix: {2}o=example.org
       olcSuffix: {3}o=The Example Company
       olcSuffix: {4}o=example,c=us

   Note that matching against an ordering-prefix can also be done in
   Compare operations and Search filters.  E.g., the filter
   &quot;(olcSuffix={4})&quot; would match all entries with at least 5 olcSuffix
   values.

4.3.  Ordered Siblings

   The rules for Ordered Siblings are basically the same as for Ordered
   Values, except instead of working primarily with the Modify request,
   the operations of interest here are Add, Delete, and ModRDN.

   Given these entries:

   dn: olcDatabase={0}config,cn=config
   olcDatabase: {0}config
   objectClass: olcDatabaseConfig
   olcSuffix: {0}cn=config


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   dn: olcDatabase={1}bdb,cn=config
   olcDatabase: {1}bdb
   objectClass: olcDatabaseConfig
   olcSuffix: {0}dc=example,dc=com

   We can perform these operations:

   1.  Add a new entry with no ordering-prefix:
       dn: olcDatabase=hdb,cn=config
       changetype: add
       olcDatabase: hdb
       objectClass: olcDatabaseConfig
       olcSuffix: {0}dc=example,dc=org
       The resulting entry will be:
       dn: olcDatabase={2}hdb,cn=config
       olcDatabase: {2}hdb
       objectClass: olcDatabaseConfig
       olcSuffix: {0}dc=example,dc=org

   2.  Continuing on with these three entries, we can add another entry
       with a specific ordering-prefix:
       dn: olcDatabase={1}ldif,cn=config
       changetype: add
       olcDatabase: {1}ldif
       objectClass: olcDatabaseConfig
       olcSuffix: {0}o=example.com
       This would give us four entries, whose DNs are:

          dn: olcDatabase={0}config,cn=config

          dn: olcDatabase={1}ldif,cn=config

          dn: olcDatabase={2}bdb,cn=config

          dn: olcDatabase={3}hdb,cn=config

   3.  Issuing a ModRDN request will cause multiple entries to be
       renamed:
       dn: olcDatabase={1}ldif,cn=config
       changetype: modrdn
       newrdn: olcDatabase={99}ldif
       deleteoldrdn: 1
       The resulting entries would be named:

          dn: olcDatabase={0}config,cn=config

          dn: olcDatabase={1}bdb,cn=config


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          dn: olcDatabase={2}hdb,cn=config

          dn: olcDatabase={3}ldif,cn=config

   4.  As may be expected, a Delete request will also rename the
       remaining entries:
       dn: olcDatabase={1}bdb,cn=config
       changetype: delete
       The remaining entries would be named:

          dn: olcDatabase={0}config,cn=config

          dn: olcDatabase={1}hdb,cn=config

          dn: olcDatabase={2}ldif,cn=config


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5.  Security Considerations

   General LDAP security considerations [RFC3377] apply.


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6.  Normative References

   [RFC2119]  Bradner, S., &quot;Key words for use in RFCs to Indicate
              Requirement Levels&quot;, BCP 14, RFC 2119, March 1997.

   [RFC2252]  Wahl, M., Coulbeck, A., Howes, T., and S. Kille,
              &quot;Lightweight Directory Access Protocol (v3): Attribute
              Syntax Definitions&quot;, RFC 2252, December 1997.

   [RFC3377]  Hodges, J. and R. Morgan, &quot;Lightweight Directory Access
              Protocol (v3): Technical Specification&quot;, RFC 3377,
              September 2002.

   [RFC3383]  Zeilenga, K., &quot;Internet Assigned Numbers Authority (IANA)
              Considerations for the Lightweight Directory Access
              Protocol (LDAP)&quot;, RFC 3383, September 2002.

   [X680]     International Telecommunications Union, &quot;Abstract Syntax
              Notation One (ASN.1): Specification of basic notation&quot;,
              ITU-T Recommendation X.680, July 2002.


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Appendix A.  IANA Considerations

   In accordance with [RFC3383] (what needs to be done here?) .  We
   probably need an OID for advertising in supportedFeatures.


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Author's Address

   Howard Chu
   Symas Corp.
   18740 Oxnard Street, Suite 313A
   Tarzana, California  91356
   USA

   Phone: +1 818 757-7087
   Email: hyc@symas.com


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Full Copyright Statement

   Copyright (C) The Internet Society (2006).

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   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

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