INTERNET-DRAFT Kurt D. Zeilenga
Intended Category: Standard Track OpenLDAP Foundation
Expires in six months 10 February 2005
LDAP Absolute True and False Filters
<draft-zeilenga-ldap-t-f-10.txt>
Status of this Memo
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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.
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) which do not necessarily have 'objectClass'
attributes. That is, where "(objectClass=*)" may evaluate to False.
While 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 [Roadmap].
This documents extends LDAPv3 to support absolute True and False
assertions by allowing empty 'and' and 'or' in Search filters
[Protocol] and extends the filter string representation [Filters] to
allow empty filter lists.
It is noted that certain search operations, such as those used to
retrieve subschema information [Models], 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).
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 represented by the string "(&)".
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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' [RFC3674]
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 is not
believed to raise any new security considerations.
Implementors of this (or any) LDAPv3 extension should be familiar with
general LDAPv3 security considerations [Roadmap].
4. IANA Considerations
Registration of this feature is requested [BCP64bis].
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 <kurt@openldap.org>
Usage: Feature
Specification: RFC XXXX
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. Author's Address
Kurt D. Zeilenga
OpenLDAP Foundation
<Kurt@OpenLDAP.org>
6. References
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[[Note to the RFC Editor: please replace the citation tags used in
referencing Internet-Drafts with tags of the form RFCnnnn where
possible.]]
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14 (also RFC 2119), March 1997.
[Roadmap] Zeilenga, K. (editor), "LDAP: Technical Specification
Road Map", draft-ietf-ldapbis-roadmap-xx.txt, a work in
progress.
[Protocol] Sermersheim, J. (editor), "LDAP: The Protocol",
draft-ietf-ldapbis-protocol-xx.txt, a work in progress.
[Models] Zeilenga, K. (editor), "LDAP: Directory Information
Models", draft-ietf-ldapbis-models-xx.txt, a work in
progress.
[Filters] Smith, M. (editor), LDAPbis WG, "LDAP: String
Representation of Search Filters",
draft-ietf-ldapbis-filter-xx.txt, a work in progress.
[Features] Zeilenga, K., "Feature Discovery in LDAP", RFC 3674,
December 2003.
6.2. 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.
[BCP64bis] Zeilenga, K., "IANA Considerations for LDAP",
draft-ietf-ldapbis-bcp64-xx.txt, a work in progress.
[RFC3494] Zeilenga, K., "Lightweight Directory Access Protocol
version 2 (LDAPv2) to Historic Status", RFC 3494, March
2003.
[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).
Zeilenga LDAP True & False Filters [Page 4]
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[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.
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Zeilenga LDAP True & False Filters [Page 5]
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Zeilenga LDAP True & False Filters [Page 6]
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