Internet DRAFT - draft-chu-ldap-xordered
draft-chu-ldap-xordered
Network Working Group H. Chu
Internet-Draft Symas Corp.
Expires: November 4, 2006 May 3, 2006
Ordered Entries and Values in LDAP
draft-chu-ldap-xordered-00.txt
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
As LDAP is used more extensively for managing various kinds of data,
one often encounters a need to preserve both the ordering and the
content of data, despite the inherently unordered structure of
entries and attribute values in the directory. This document
describes a scheme to attach ordering information to attributes in a
directory so that the ordering may be preserved and propagated to
other LDAP applications.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . 4
3. Ordering Extension . . . . . . . . . . . . . . . . . . 5
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Encoding . . . . . . . . . . . . . . . . . . . . . . . 5
3.3. Ordering Properties . . . . . . . . . . . . . . . . . 6
4. Examples . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Sample Schema . . . . . . . . . . . . . . . . . . . . 8
4.2. Ordered Values . . . . . . . . . . . . . . . . . . . . 8
4.3. Ordered Siblings . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . 13
6. Normative References . . . . . . . . . . . . . . . . . 13
Appendix A. IANA Considerations . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . 16
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1. Introduction
Information in LDAP directories is usually handled by applications in
the form of ordered lists, which tends to encourage application
developers to assume they are maintained as such, i.e., it is assumed
that information stored in a particular order will always be
retrieved and presented in that same order. The fact that directory
attributes actually store sets of values, which are inherently
unordered, often causes grief to users migrating their data into
LDAP. Similar concerns arise over the order in which entries
themselves are stored and retrieved from the directory.
This document describes a schema extension that may be used in LDAP
attribute definitions to store ordering information along with the
attribute values, so that the ordering can be recovered when
retrieved by an LDAP client. The extension also provides automated
management of this ordering information to ease manipulation of the
ordered values.
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2. Conventions
Imperative keywords defined in [RFC2119] are used in this document,
and carry the meanings described there.
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3. Ordering Extension
3.1. Overview
The "X-ORDERED" schema extension is added to an
AttributeTypeDescription to signify the use of this ordering
mechanism. The extension has two variants, selected by either the
'VALUES' or 'SIBLINGS' qdstrings. In general this extension is only
compatible with AttributeTypes that have a string-oriented syntax.
The "X-ORDERED 'VALUES'" extension is used with multi-valued
attributes to maintain the order of multiple values of a given
attribute. For example, this feature is useful for storing data such
as access control rules, which must be evaluated in a specific order.
If the access control information is stored in a multi-valued
attribute without a means of preserving the the order of the rules,
the access control rules cannot be evaluated properly. As the use of
LDAP to store security policy and access control information becomes
more prevalent, the necessity of this feature continues to grow.
The "X-ORDERED 'SIBLINGS'" extension is used with single-valued
attributes to maintain the order of all the onelevel children of a
parent entry. That is, ordering will be maintained for all the child
entries whose RDNs are all of the same AttributeType. The motivation
for this feature is much the same as for the 'VALUES' feature.
Sometimes the information with the ordering dependency is too complex
or highly structured to be conveniently stored in values of a multi-
valued attribute. For example, one could store a prioritized list of
servers as a set of separate entries, each entry containing separate
attributes for a URL, a set of authentication credentials, and
various other parameters. Using the 'SIBLINGS' feature with the
attribute in the entries' RDNs would ensure that when obtaining the
list of these entries, the list is returned in the intended order.
3.2. Encoding
Ordering information is encoded by prepending a value's ordinal index
to each value, enclosed in braces. The following BNF specifies the
encoding. It uses elements defined in [RFC2252].
d = "0" / "1" / "2" / "3" / "4" / "5" / "6" / "7" / "8" / "9"
numericstring = 1*d
ordering-prefix = "{" numericstring "}"
value = <any sequence of octets>
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ordered-value = ordering-prefix value
The ordinals are zero-based and increment by one for each value.
Note that when storing ordered-values into the directory, the
ordering-prefix can usually be omitted as it will be generated
automatically. But if the original value already begins with a
sequence of characters in the form of an ordering-prefix, then an
ordering-prefix must always be provided with that value, otherwise
the value will be processed and stored incorrectly.
Using this extension on an attribute requires that ordering-prefix is
a legal value of the LDAP syntax of that attribute.
3.3. Ordering Properties
Since the ordering-prefix is stored with the attribute values, it
will be propagated to any clients or servers that access the data.
Servers implementing this scheme SHOULD sort the values according to
their ordering-prefix before returning them in search results.
The presence of the ordering extension alters the matching rules that
apply to the attribute:
When presented with an AssertionValue that does not have an
ordering-prefix, the ordering-prefix in the AttributeValue is
ignored.
When presented with an AssertionValue that consists solely of an
ordering-prefix, only the ordering-prefix of the AttributeValue is
compared; the remainder of the value is ignored.
When presented with an AssertionValue containing both the
ordering-prefix and a value, both components are compared to
determine a match.
A side effect of these properties is that even attributes that
normally would have no equality matching rule can be matched by an
ordering-prefix.
The ordering-prefix may also be used in Modification requests to
specify which values to delete, and in which position values should
be added. When processing deletions and insertions, all of the
ordinals are recounted after each individual modification.
If a value being added does not have an ordering-prefix, it is simply
appended to the list and the appropriate ordering-prefix is
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automatically generated. Likewise if an ordering-prefix is provided
that is greater than or equal to the number of existing values.
See the examples in the next section.
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4. Examples
4.1. Sample Schema
This schema is used for all of the examples:
( EXAMPLE_AT.1 NAME 'olcDatabase'
EQUALITY caseIgnoreMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.15
SINGLE-VALUE X-ORDERED 'SIBLINGS' )
( EXAMPLE_AT.2 NAME 'olcSuffix'
EQUALITY distinguishedNameMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.12
X-ORDERED 'VALUES' )
( EXAMPLE_OC.1 NAME 'olcDatabaseConfig'
SUP top STRUCTURAL
MAY ( olcDatabase $ olcSuffix ) )
4.2. Ordered Values
Given this entry:
dn: olcDatabase={1}bdb,cn=config
olcDatabase: {1}bdb
objectClass: olcDatabaseConfig
olcSuffix: {0}dc=example,dc=com
olcSuffix: {1}o=example.com
olcSuffix: {2}o=The Example Company
olcSuffix: {3}o=example,c=us
We can perform these Modify operations:
1. dn: olcDatabase={1}bdb,cn=config
changetype: modify
delete: olcSuffix
olcSuffix: {0}
-
This operation deletes the first olcSuffix, regardless of its
value. All other values are bumped up one position. The
olcSuffix attribute will end up containing:
olcSuffix: {0}o=example.com
olcSuffix: {1}o=The Example Company
olcSuffix: {2}o=example,c=us
2. Starting from the original entry, we could issue this change
instead:
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delete: olcSuffix
olcSuffix: o=example.com
-
This operation deletes the olcSuffix that matches the value,
regardless of its ordering-prefix. The olcSuffix attribute will
contain:
olcSuffix: {0}dc=example,dc=com
olcSuffix: {1}o=The Example Company
olcSuffix: {2}o=example,c=us
3. Again, starting from the original entry, we could issue this
change:
delete: olcSuffix
olcSuffix: {2}o=The Example Company
-
Here both the ordering-prefix and the value must match, otherwise
the Modify would fail with noSuchAttribute. In this case the
olcSuffix attribute results in:
olcSuffix: {0}dc=example,dc=com
olcSuffix: {1}o=example.com
olcSuffix: {2}o=example,c=us
4. Adding a new value without an ordering-prefix simply appends:
add: olcSuffix
olcSuffix: o=example.org
-
The resulting attribute would be:
olcSuffix: {0}dc=example,dc=com
olcSuffix: {1}o=example.com
olcSuffix: {2}o=The Example Company
olcSuffix: {3}o=example,c=us
olcSuffix: {4}o=example.org
5. Adding a new value with an ordering-prefix inserts into the
specified position:
add: olcSuffix
olcSuffix: {0}o=example.org
-
The resulting attribute would be:
olcSuffix: {0}o=example.org
olcSuffix: {1}dc=example,dc=com
olcSuffix: {2}o=example.com
olcSuffix: {3}o=The Example Company
olcSuffix: {4}o=example,c=us
6. Modifying multiple values in one operation:
add: olcSuffix
olcSuffix: {0}ou=Dis,o=example.com
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olcSuffix: {0}ou=Dat,o=example,com
-
delete: olcSuffix:
olcSuffix: {2}
olcSuffix: {1}
-
The resulting attribute would be:
olcSuffix: {0}ou=Dat,o=example,com
olcSuffix: {1}dc=example,dc=com
olcSuffix: {2}o=example.com
olcSuffix: {3}o=The Example Company
olcSuffix: {4}o=example,c=us
7. If the Adds and Deletes in the previous example were done in the
opposite order:
delete: olcSuffix:
olcSuffix: {2}
olcSuffix: {1}
-
add: olcSuffix
olcSuffix: {0}ou=Dis,o=example.com
olcSuffix: {0}ou=Dat,o=example,com
-
The result would be:
olcSuffix: {0}ou=Dat,o=example,com
olcSuffix: {1}ou=Dis,o=example.com
olcSuffix: {2}o=example.org
olcSuffix: {3}o=The Example Company
olcSuffix: {4}o=example,c=us
Note that matching against an ordering-prefix can also be done in
Compare operations and Search filters. E.g., the filter
"(olcSuffix={4})" would match all entries with at least 5 olcSuffix
values.
4.3. Ordered Siblings
The rules for Ordered Siblings are basically the same as for Ordered
Values, except instead of working primarily with the Modify request,
the operations of interest here are Add, Delete, and ModRDN.
Given these entries:
dn: olcDatabase={0}config,cn=config
olcDatabase: {0}config
objectClass: olcDatabaseConfig
olcSuffix: {0}cn=config
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dn: olcDatabase={1}bdb,cn=config
olcDatabase: {1}bdb
objectClass: olcDatabaseConfig
olcSuffix: {0}dc=example,dc=com
We can perform these operations:
1. Add a new entry with no ordering-prefix:
dn: olcDatabase=hdb,cn=config
changetype: add
olcDatabase: hdb
objectClass: olcDatabaseConfig
olcSuffix: {0}dc=example,dc=org
The resulting entry will be:
dn: olcDatabase={2}hdb,cn=config
olcDatabase: {2}hdb
objectClass: olcDatabaseConfig
olcSuffix: {0}dc=example,dc=org
2. Continuing on with these three entries, we can add another entry
with a specific ordering-prefix:
dn: olcDatabase={1}ldif,cn=config
changetype: add
olcDatabase: {1}ldif
objectClass: olcDatabaseConfig
olcSuffix: {0}o=example.com
This would give us four entries, whose DNs are:
dn: olcDatabase={0}config,cn=config
dn: olcDatabase={1}ldif,cn=config
dn: olcDatabase={2}bdb,cn=config
dn: olcDatabase={3}hdb,cn=config
3. Issuing a ModRDN request will cause multiple entries to be
renamed:
dn: olcDatabase={1}ldif,cn=config
changetype: modrdn
newrdn: olcDatabase={99}ldif,cn=config
deleteoldrdn: 1
The resulting entries would be named:
dn: olcDatabase={0}config,cn=config
dn: olcDatabase={1}bdb,cn=config
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dn: olcDatabase={2}hdb,cn=config
dn: olcDatabase={3}ldif,cn=config
4. As may be expected, a Delete request will also rename the
remaining entries:
dn: olcDatabase={1}bdb,cn=config
changetype: delete
The remaining entries would be named:
dn: olcDatabase={0}config,cn=config
dn: olcDatabase={1}hdb,cn=config
dn: olcDatabase={2}ldif,cn=config
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5. Security Considerations
General LDAP security considerations [RFC3377] apply.
6. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2252] Wahl, M., Coulbeck, A., Howes, T., and S. Kille,
"Lightweight Directory Access Protocol (v3): Attribute
Syntax Definitions", RFC 2252, December 1997.
[RFC3377] Hodges, J. and R. Morgan, "Lightweight Directory Access
Protocol (v3): Technical Specification", RFC 3377,
September 2002.
[RFC3383] Zeilenga, K., "Internet Assigned Numbers Authority (IANA)
Considerations for the Lightweight Directory Access
Protocol (LDAP)", BCP 64, RFC 3383, September 2002.
[X680] International Telecommunications Union, "Abstract Syntax
Notation One (ASN.1): Specification of basic notation",
ITU-T Recommendation X.680, July 2002.
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Appendix A. IANA Considerations
In accordance with [RFC3383] (what needs to be done here?) . We
probably need an OID for advertising in supportedFeatures.
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Author's Address
Howard Chu
Symas Corp.
18740 Oxnard Street, Suite 313A
Tarzana, California 91356
USA
Phone: +1 818 757-7087
Email: hyc@symas.com
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