Internet-Draft                                      David Chadwick
LDAPExt WG                                         University of Salford
Intended Category: Standards Track                     Sean Mullan
                                                                  Sun
Microsystems
Expires: 8 March 2000                             8 September 1999

Returning Matched Values with LDAPv3
<draft-ietf-ldapext-matchedval-01.txt>

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ABSTRACT

This document describes a control for the Lightweight Directory
Access Protocol v3 that is used to return a subset of attribute
values from an entry, specifically, only those values that
contributed to the search filter evaluating to TRUE. Without support
for this control, a client must retrieve all of an attribute's values
and search for specific values locally.

. Introduction

When reading an attribute from an entry using LDAP v2 [1] or LDAPv3
[2], it is normally only possible to read either the attribute type,
or the attribute type and all its values. It is not possible to
selectively read just a few of the attribute values. If an attribute
holds many values, for example, the userCertificate attribute, or the
subschema publishing operational attributes objectClasses and
attributeTypes [3], then it may be desirable for the user to be able
to selectively retrieve a subset of the values, specifically, those
attribute values that match the selection criteria as specified by
the user in the filter. Without the control specified in this
[ID/standard] a client must read all of the attribute's values and
filter out the unwanted values, necessitating the client to implement
the matching rules. It also requires the client to potentially read
and process many irrelevant values, which can be inefficient if the
values are large or complex, or there are many values stored per
attribute.

This Internet Draft specifies an LDAPv3 control to enable a user to
return only those values that matched (i.e. returned TRUE to) one or
more elements of the Search filter. This control can be especially
useful when used in conjunction with extensible matching rules that
match on one or more components of complex binary attribute values.

The control has been described in such a way as to be fully
compatible with the matchedValuesOnly boolean of the X.500 DAP [4]
Search argument, as amended in the latest version [6].

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 RFC 2119 [5].

. The matchedValuesOnly Control

The matchedValuesOnly control MAY be critical or non-critical as
determined by the user. It is only applicable to the Search
operation, and SHALL be ignored by the server if it is present on any
other LDAP operation (even if marked critical on such operations).

The object identifier for this control is 1.2.826.0.1.3344810.2.2

The controlValue is absent.

If the server supports this control, the server MUST make use of the
control as follows:

(1) If the typesOnly parameter of the Search Request is TRUE,
the control has no effect and the Search Request SHOULD be
processed as if the control had not been specified.

(2) If the attributes parameter of the Search Request consists
of a list containing only the attribute with OID "1.1"
(specifying that no attributes are to be returned), the control
has no effect and the Search Request SHOULD be processed as if
the control had not been specified.

(3) For each attribute listed in the attributes parameter of the
Search Request, the server MUST apply the control as follows:

i) Every attribute value that evaluates TRUE against one or
more filters, excluding the ignored filters (see below),
is logically marked by the server as contributing to the
filter matching.
ii) Attributes that have no values marked as contributing,
have all their values returned to the user.
iii) Attributes that have one or more values marked as
contributing have only the contributing values returned to
the user, whilst the other values of the same attribute
(if there are any) are not returned.

Certain filters are ignored for the purposes of marking the attribute
values as contributing. These are:

the ôpresentö filter, since this filter does not test against
any attribute values;
the ônotö filter, since this would have the effect of marking
all the attribute values except the one(s) that matched the
non-negated filter.

. Relationship to X.500

The matchedValuesOnly control defined in this document is derived
from the matchedValuesOnly boolean parameter of the X.511 (93) DAP
Search operation [4]. Note however that in X.511 (93), the
matchedValuesOnly parameter is ignored when used with an "equality"
match FilterItem, and so the user must use the extensibleMatch filter
along with the equality matching rule if only matched values are
wanted with equality matching. This slightly spurious equality match
restriction has been removed from the 2000 version of X.511 [6]. For
LDAP servers acting as a gateway to an X.500 directory, the matched
valuesOnly control can be directly mapped onto the X.511
matchedValuesOnly Search parameter as follows:

(1) If the matchedValuesOnly control is specified, the
matchedValuesOnly DAP parameter MUST be set to true. If the
control criticality value is TRUE then bit 17 of the DAP
criticalExtensions MUST be set.

(2) If an equality matching rule is specified in the filter of
the LDAPv3 search operation, then if operating with a pre-2000
edition DSA, the corresponding equality FilterItem contained in
the X.511 filter parameter MUST NOT be used, but rather the
extensibleMatch filter item MUST be used instead (the assertion
consisting of the equality matching rule, the attribute type to
match on, and the asserted value). When operating with DSAs
that support the 2000 DAP enhancement, the equality FilterItem
MAY be used.

. Examples

(1) The first example simply shows how the control can be used to
selectively read a subset of attribute values.

The entry below represents a groupOfNames object class containing
several members from different organizations.

cn: Cross Organizational Standards Body
member: cn=joe, o=acme
member: cn=alice, o=acme
member: cn=bob, o=foo
member: cn=sue, o=bar

An LDAP search operation is specified with a baseObject set to the
DN of the entry, a baseObject scope, a filter set to
"member=*o=acme", and the list of attributes to be returned set to
"member". In addition, a matchedValuesOnly control is attached to the
search request.

The search results returned by the server would consist of the
following entry:

cn: Cross Organizational Standards Body
member: cn=joe, o=acme
member: cn=alice, o=acme

(2) The second example shows how the control has no effect on
attributes that do not participate in the search filter.

The entries below represent inetOrgPerson [7] object classes located
below some distinguished name in the directory.

cn: Sean Mullan
mail: sean.mullan@sun.com
mail: mullan@east.sun.com
telephoneNumber: +1 781 442 0926
telephoneNumber: 555-9999

cn: David Chadwick
mail: d.w.chadwick@salford.ac.uk

An LDAP search operation is specified with a baseObject set to the
DN of the entry, a subtree scope, a filter set to
"(|(mail=sean.mullan@sun.com)(mail=d.w.chadwick@salford.ac.uk))", and
the list of attributes to be returned set to "mail telephoneNumber".
In addition, a matchedValuesOnly control is attached to the search
request.

The search results returned by the server would consist of the
following entries:

cn: Sean Mullan
mail: sean.mullan@sun.com
telephoneNumber: +1 781 442 0926
telephoneNumber: 555-9999

cn: David Chadwick
mail: d.w.chadwick@salford.ac.uk

Note that the control has no effect on the values returned for the
"telephoneNumber" attribute (all of the values are returned), since
it did not participate in the search filter.

. Security Considerations

This Internet Draft does not discuss security issues at all.

Note that attribute values MUST only be returned if the access
controls applied by the LDAP server allow them to be returned, and in
this respect the effect of the matchedValuesOnly control is of no
consequence.

Note that the matchedValuesOnly control may have a positive effect on
the deployment of public key infrastructures. Certain PKI operations,
like searching for specific certificates, become more practical (when
combined with X.509 certificate matching rules at the server) and
more scalable, since the control avoids the downloading of
potentially large numbers of irrelevant certificates which would have
to be processed and filtered locally (which in some cases is very
difficult to perform).

. Copyright

Copyright (C) The Internet Society (date). All Rights Reserved.

This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works.  However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.

The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

. References

[] Yeong, W., Howes, T., and Kille, S. "Lightweight Directory Access
Protocol", RFC 1777, March 1995.
[2] M. Wahl, T. Howes, S. Kille, "Lightweight Directory Access
Protocol (v3)", Dec. 1997, RFC 2251
[3] M. Wahl, A. Coulbeck, T. Howes, S. Kille, ôLightweight Directory
Access Protocol (v3): Attribute Syntax Definitionsö, RFC 2252, Dec
1997
[4] ITU-T Rec. X.511, "The Directory: Abstract Service Definition",
1993.
[5] S.Bradner. "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[6] ôFPDAMs to ISO/IEC 9594 Parts 1, 2, 3, 4, 5, 6, 7 and 9 to
support the ITU-T Rec. F.510 "Automated Directory Assistance, White
Pages Service Definitions"ö, Collaborative ITU-T/SG7/Q15 and
JTC1/SC6/WG7 OSI Directory Meeting 7-15 April 1999, Orlando, USA
[7] M. Smith. "Definition of the inetOrgPerson LDAP Object Class",
Internet Draft <draft-smith-ldap-inetorgperson-03.txt>, April 1999.

. Authors Addresses

David Chadwick
IS Institute
University of Salford
Salford M5 4WT
England

Email: d.w.chadwick@salford.ac.uk

Sean Mullan
Sun Microsystems Laboratories
One Network Drive
Burlington
MA 01803-0902
USA

Tel:  +1 781 442-0926           Fax:  +1 781 442-1692
Email: sean.mullan@sun.com

Internet-Draft  Returning Matched Values with LDAPv3 8 September 1999

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