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.
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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RFC 4526 LDAP Absolute True and False Filters June 2006
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].
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.
[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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RFC 4526 LDAP Absolute True and False Filters June 2006
[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).
RFC 4526 LDAP Absolute True and False Filters June 2006
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