Network Working Group                                        K. Zeilenga
Request for Comments: 4526                           OpenLDAP Foundation
Category: Standards Track                                      June 2006


             Lightweight Directory Access Protocol (LDAP)
                   Absolute True and False Filters

Status of This Memo

  This document specifies an Internet standards track protocol for the
  Internet community, and requests discussion and suggestions for
  improvements.  Please refer to the current edition of the "Internet
  Official Protocol Standards" (STD 1) for the standardization state
  and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

  Copyright (C) The Internet Society (2006).

Abstract

  This document extends the Lightweight Directory Access Protocol
  (LDAP) to support absolute True and False filters based upon similar
  capabilities found in X.500 directory systems.  The document also
  extends the String Representation of LDAP Search Filters to support
  these filters.

Table of Contents

  1. Background ......................................................1
  2. Absolute True and False Filters .................................2
  3. Security Considerations .........................................2
  4. IANA Considerations .............................................3
  5. References ......................................................3
     5.1. Normative References .......................................3
     5.2. Informative References .....................................3

1.  Background

  The X.500 Directory Access Protocol (DAP) [X.511] supports absolute
  True and False assertions.  An 'and' filter with zero elements always
  evaluates to True.  An 'or' filter with zero elements always
  evaluates to False.  These filters are commonly used when requesting
  DSA-specific Entries (DSEs) that do not necessarily have
  'objectClass' attributes; that is, where "(objectClass=*)" may
  evaluate to False.




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  Although LDAPv2 [RFC1777][RFC3494] placed no restriction on the
  number of elements in 'and' and 'or' filter sets, the LDAPv2 string
  representation [RFC1960][RFC3494] could not represent empty 'and' and
  'or' filter sets.  Due to this, absolute True or False filters were
  (unfortunately) eliminated from LDAPv3 [RFC4510].

  This documents extends LDAPv3 to support absolute True and False
  assertions by allowing empty 'and' and 'or' in Search filters
  [RFC4511] and extends the filter string representation [RFC4515] to
  allow empty filter lists.

  It is noted that certain search operations, such as those used to
  retrieve subschema information [RFC4512], require use of particular
  filters.  This document does not change these requirements.

  This feature is intended to allow a more direct mapping between DAP
  and LDAP (as needed to implement DAP-to-LDAP gateways).

  In this document, the key words "MUST", "MUST NOT", "REQUIRED",
  "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
  and "OPTIONAL" are to be interpreted as described in BCP 14
  [RFC2119].

2.  Absolute True and False Filters

  Implementations of this extension SHALL allow 'and' and 'or' choices
  with zero filter elements.

  An 'and' filter consisting of an empty set of filters SHALL evaluate
  to True.  This filter is represented by the string "(&)".

  An 'or' filter consisting of an empty set of filters SHALL evaluate
  to False.  This filter is represented by the string "(|)".

  Servers supporting this feature SHOULD publish the Object Identifier
  1.3.6.1.4.1.4203.1.5.3 as a value of the 'supportedFeatures'
  [RFC4512] attribute in the root DSE.

  Clients supporting this feature SHOULD NOT use the feature unless
  they know that the server supports it.

3.  Security Considerations

  The (re)introduction of absolute True and False filters is not
  believed to raise any new security considerations.

  Implementors of this (or any) LDAPv3 extension should be familiar
  with general LDAPv3 security considerations [RFC4510].



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4.  IANA Considerations

  Registration of this feature has been completed by the IANA
  [RFC4520].

  Subject: Request for LDAP Protocol Mechanism Registration Object
  Identifier: 1.3.6.1.4.1.4203.1.5.3 Description: True/False filters
  Person & email address to contact for further information:
       Kurt Zeilenga <[email protected]> Usage: Feature Specification:
  RFC 4526 Author/Change Controller: IESG Comments: none

  This OID was assigned [ASSIGN] by OpenLDAP Foundation, under its
  IANA-assigned private enterprise allocation [PRIVATE], for use in
  this specification.

5.  References

5.1.  Normative References

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

  [RFC4510]     Zeilenga, K., Ed, "Lightweight Directory Access
                Protocol (LDAP): Technical Specification Road Map", RFC
                4510, June 2006.

  [RFC4511]     Sermersheim, J., Ed., "Lightweight Directory Access
                Protocol (LDAP): The Protocol", RFC 4511, June 2006.

  [RFC4512]     Zeilenga, K., "Lightweight Directory Access Protocol
                (LDAP): Directory Information Models", RFC 4512, June
                2006.

  [RFC4515]     Smith, M., Ed. and T. Howes, "Lightweight Directory
                Access Protocol (LDAP): String Representation of Search
                Filters", RFC 4515, June 2006.

5.2.  Informative References

  [RFC1777]     Yeong, W., Howes, T., and S. Kille, "Lightweight
                Directory Access Protocol", RFC 1777, March 1995.

  [RFC1960]     Howes, T., "A String Representation of LDAP Search
                Filters", RFC 1960, June 1996.

  [RFC3494]     Zeilenga, K., "Lightweight Directory Access Protocol
                version 2 (LDAPv2) to Historic Status", RFC 3494, March
                2003.



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  [RFC4520]     Zeilenga, K., "Internet Assigned Numbers Authority
                (IANA) Considerations for the Lightweight Directory
                Access Protocol (LDAP)", BCP 64, RFC 4520, June 2006.

  [X.500]       International Telecommunication Union -
                Telecommunication Standardization Sector, "The
                Directory -- Overview of concepts, models and
                services," X.500(1993) (also ISO/IEC 9594-1:1994).

  [X.501]       International Telecommunication Union -
                Telecommunication Standardization Sector, "The
                Directory -- Models," X.501(1993) (also ISO/IEC 9594-
                2:1994).

  [X.511]       International Telecommunication Union -
                Telecommunication Standardization Sector, "The
                Directory: Abstract Service Definition", X.511(1993)
                (also ISO/IEC 9594-3:1993).

  [ASSIGN]      OpenLDAP Foundation, "OpenLDAP OID Delegations",
                http://www.openldap.org/foundation/oid-delegate.txt.

  [PRIVATE]     IANA, "Private Enterprise Numbers",
                http://www.iana.org/assignments/enterprise-numbers.

Author's Address

  Kurt D. Zeilenga
  OpenLDAP Foundation

  EMail: [email protected]




















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Full Copyright Statement

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Acknowledgement

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  Administrative Support Activity (IASA).







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