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draft-ietf-boreham-numsubordinates-00.txt
This is a short draft which describes a feature
already supported by Netscape and MessagingDirect server
products. We welcome review comments from the list.
INTERNET-DRAFT David Boreham, Netscape
Steve Kille, MessagingDirect Ltd.
Individual Submission 10 June, 1999
numSubordinates LDAP Operational Attribute
draft-ietf-boreham-numsubordinates-00.txt
This document expires on 9 December 1999
1. Status of this Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026. Internet-Drafts are working docu-
ments 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 Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
2. Abstract
This document decibes an LDAP operational attribute named "numSubordi-
nates". The purpose of this attribute is to allow clients to determine
efficiently the number of entries immediately below (in the DIT), any
particular directory entry.
3. Background
Experience has shown that where an LDAP client wishes to "browse" the
Directory Information Tree (DIT), it is useful to be able to determine
how many entries exist which are immediate subordinates of a particular
entry. Knowledge of this information allows the client to display UI to
the effect that "there are too many entries in this container to
display". Only by waiting for some timeout interval would it be possi-
ble to come to this conclusion without knowing the subordinate count in
advance. Such a timeout leads to poor user experience. Similarly, UI
which displays the DIT complete with the content count of each container
Boreham and Kille [Page 1]
RFC DRAFT June 1999
entry becomes feasible. In addition, easy and efficient access to
subordinate count information permits client tools to analyse the DIT,
for example to determine where special server indices or precomputed
search result sets should be maintained to give optimum performance.
The key words "MUST", "SHOULD", and "MAY" used in this document are to
be interpreted as described in [Bradner97].
4. Attribute Definition
The numSubordinates attribute is defined as follows in RFC2252 then
X.520 ASN.1 format:
( 1.3.1.1.4.1.453.16.2.103 NAME 'numSubordinates'
DESC 'count of immediate subordinates'
EQUALITY integerMatch ORDERING integerOrderingMatch
SYNTAX 1.3.6.1.4.1.453.16.2.103
SINGLE-VALUE NO-USER-MODIFICATION USAGE directoryOperation )
numSubordinates ATTRIBUTE ::= {
WITH SYNTAX INTEGER
USAGE directoryOperation
SINGLEVALUED TRUE
NO USER MODIFICATION TRUE
ID {dod internet(1) private(4)
enterprises(1) isode-consortium(453)
ic-dsa(16) ic-dsa-at(2) 103}
}
Every entry in the DIT MAY have a numSubordinates operational attribute
the contents of which indicate how many immediate subordinates that
entry has. For example, a leaf entry would have numSubordinates equal to
"0". Entry "ou=People, o=ace industry, c=us" in a DIT where the contents
of that container comprises 1000 leaf entries, would have numSubordi-
nates equal to "1000".
Server support for the numSubordinates attribute is on a per-entry
basis. That is, the presence of the attribute indicates that its value
is correct, while the absence of the attribute indicates nothing other
than the lack of support for the attribute. Consequently, absence of the
numSubordinates attribute does not imply that there are no subordinates.
5. Client-Server Interaction
Clients may read the value of the numSubordinates attribute by perform-
ing a regular LDAP search operation[LDAPv3], while specifying numSubor-
dinates as one of the requested attributes. Note that an operational
attribute such as numSubordinates will not be returned to the client
unless explicitly requested.
Boreham and Kille [Page 2]
RFC DRAFT June 1999
Clients can not modify the contents of the numSubordinates attribute.
Servers MUST refuse to allow such modifications and SHOULD return the
unwilling to perform status code.
Servers MUST ensure that the value returned in the numSubordinates atti-
bute to clients is consistent with the view that client has of other
server contents. For example, is it NOT permissible to delay updating
the numSubordinates count for some container entry until some time after
subordinates have been added or deleted. This would lead to the poten-
tial for a client to see an inconsistency between the numSubordinates
value reported for an entry and the number of entries that same client
had added as subordinates.
6. Relationship to hasSubordinates
The X.500 hasSubordinates operational attribute[ITU-X501] can be
regarded as indicating whether numSubordinates has a non-zero value for
the same entry. This leads to the potential for optimization in a server
implementation, in that it isn't necessary to store both values.
7. Security Considerations
Any client which is able to read the numSubordinates attribute may be
able to discover more about the contents of the DIT than would be possi-
ble without access to that attribute. Consequently server implementers
are advised to provide an access control mechanism which can be used to
restrict access to numSubordinates. For servers which already have an
attribute-level access control facility, this might involve no more than
ensuring that numSubordinates falls within that existing scheme.
8. References
[ITU-X501]
The Directory: Models. ITU-T Recommendation X.501, 1997, section
section 13.4.4.
[LDAPv3]
Wahl, M, S. Kille and T. Howes, "Lightweight Directory Access Pro-
tocol (v3)", Internet Standard, December, 1997. Available as
RFC2251.
[RFC2252]
Wahl et al, Lightweight Directory Access Protocol (v3): Attribute
Syntax Definitions. Available as RFC2252.
[ITU-X520]
The Directory: Selected Attribute Types. ITU-T Recommendation
X.520, 1997.
Boreham and Kille [Page 3]
RFC DRAFT June 1999
[Bradner97]
Bradner, Scott, "Key Words for use in RFCs to Indicate Requirement
Levels", Internet Draft, March, 1997. Available as RFC2119.
9. Authors' Addresses
David Boreham Steve Kille
Netscape Communications Corp. MessagingDirect
501 E. Middlefield Road The Dome, The Square
Mountain View, CA 94043, USA Richmond
+1 650 937-5206 Surrey, TW9 1DT, UK
dboreham@netscape.com +44 181 332 9091
Steve.Kille@messagingdirect.com
This document expires on 9 December 1999
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