





INTERNET-DRAFT                                      Kurt D. Zeilenga
Intended Category: Standard Track                OpenLDAP Foundation
Expires in six months                                    17 May 2002



                         LDAP True/False Filters
                     <draft-zeilenga-ldap-t-f-02.txt>


Status of this Memo

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

  This document is intended to be, after appropriate review and
  revision, submitted to the RFC Editor as a Standard Track document.
  Distribution of this memo is unlimited.  Technical discussion of this
  document will take place on the IETF LDAP Extensions Working Group
  mailing list <ietf-ldapext@netscape.com>.  Please send editorial
  comments directly to the author <Kurt@OpenLDAP.org>.

  Internet-Drafts are working documents of the Internet Engineering Task
  Force (IETF), its areas, and its working groups.  Note that other
  groups may also distribute working documents as Internet-Drafts.
  Internet-Drafts are draft documents valid for a maximum of six months
  and may be updated, replaced, or obsoleted by other documents at any
  time.  It is inappropriate to use Internet-Drafts as reference
  material or to cite them other than as ``work in progress.''

  The list of current Internet-Drafts can be accessed at
  <http://www.ietf.org/ietf/1id-abstracts.txt>. The list of
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  <http://www.ietf.org/shadow.html>.

  Copyright 2002, The Internet Society.  All Rights Reserved.

  Please see the Copyright section near the end of this document for
  more information.


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.



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1.  Background and Intended Use

  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) which do not necessarily have objectClass
  attributes.  That is, where "(objectClass=*)" may evaluate to False.

  While LDAPv2 [RFC1777] placed no restriction on the number of elements
  in 'and' and 'or' filter sets, the LDAPv2 string representation
  [RFC1960] could not represent empty 'and' and 'or' filter sets.  Due
  to this, LDAPv3 [RFC2251] required 'and' and 'or' filter sets to have
  at least one element.  Hence, LDAPv3 does not provide absolute True or
  False filters.

  This documents extends LDAPv3 [RFC2251] to support absolute True and
  False matches by allowing empty 'and' and 'or' and extends the filter
  string representation [RFC2254] to allow empty filter lists.

  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
  "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
  document 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 to represented by the string "(&)".

  An 'or' Filter consisting of an empty set of filters SHALL evaluate to
  False.  This filter is to 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 [FEATURES]
  attribute in the root DSE.

  Clients supporting this feature SHOULD NOT use the feature unless they
  have knowledge the server supports it.


3.  Security Considerations

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



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


4.  IANA Considerations

  No IANA assignments are requested.

  This document uses the OID 1.3.6.1.4.1.4203.1.5.3 to identify the
  feature described above.  This OID was assigned [ASSIGN] by OpenLDAP
  Foundation under its IANA assigned private enterprise allocation
  [PRIVATE] for use in this specification.


5.  Author's Address

  Kurt D. Zeilenga
  OpenLDAP Foundation
  <Kurt@OpenLDAP.org>


6. Normative References

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

  [RFC2251]  M. Wahl, T. Howes, S. Kille, "Lightweight Directory Access
             Protocol (v3)", RFC 2251, December 1997.

  [RFC2254]  T. Howes, "A String Representation of LDAP Search Filters",
             RFC 2254, December 1997.

  [LDAPTS]   J. Hodges, R. Morgan, "Lightweight Directory Access
             Protocol (v3): Technical Specification",
             draft-ietf-ldapbis-ldapv3-ts-xx.txt (a work in progress).

  [FEATURES] K. Zeilenga, "Feature Discovery in LDAP",
             draft-zeilenga-ldap-features-xx.txt (a work in progress).


7. Informative References

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

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




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  [X.500]    ITU-T Rec. X.500, "The Directory: Overview of Concepts,
             Models and Service", 1993.

  [X.511]    ITU-T Rec. X.511, "The Directory: Abstract Service
             Definition", 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.



Copyright 2002, The Internet Society.  All Rights Reserved.

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