INTERNET-DRAFT Editor: Kurt D. Zeilenga
Intended Category: Standard Track OpenLDAP Foundation
Expires in six months 12 August 2002
Obsoletes: RFC 2251, RFC 2252, RFC 2256
LDAP: Directory Information Models
<draft-ietf-ldapbis-models-02.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.
This document is intended to be published as a Standard Track RFC.
Distribution of this memo is unlimited. Technical discussion of this
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mailing list <ietf-ldapbis@openldap.org>. Please send editorial
comments directly to the author <Kurt@OpenLDAP.org>.
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Copyright 2002, The Internet Society. All Rights Reserved. Please
see the Copyright section near the end of this document for more
information.
Abstract
The Lightweight Directory Access Protocol (LDAP) is an Internet
protocol for accessing distributed directory services which act in
accordance with X.500 data and service models. This document
describes the X.500 Directory Information Models, as used in LDAP.
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Table of Contents
Status of this Memo 1
Abstract
Table of Contents 2
1. Introduction 4
1.1. Relationship to Other LDAP Specifications
1.2. Conventions 5
1.3. Common ABNF Productions
2. Model of Directory User Information 7
2.1. The Directory Information Tree
2.2. Naming of Entries 8
2.2.1. Relative Distinguished Names
2.2.2. Distinguished Names
2.2.3. Alias Names
2.3. Structure of an Entry
2.4. Object Classes 9
2.4.1. Abstract Object Classes 10
2.4.2. Structural Object Classes
2.4.3. Auxiliary Object Classes 11
2.5. Attribute Descriptions
2.5.1. Attribute Types 12
2.5.2. Attribute Options 13
2.5.2.1. Tagging Options
2.5.3. Attribute Description Hierarchies 14
2.5.4. Attribute Values 15
2.6. Alias Entries
2.6.1. 'alias' 16
2.6.2. 'aliasObjectName'
3. Directory Administrative and Operational Information
3.1. Subtrees
3.2. Subentries 17
3.3. The 'objectClass' attribute
3.4. Operational attributes 18
3.4.1. 'creatorsName'
3.4.2. 'createTimestamp' 19
3.4.3. 'modifiersName'
3.4.4. 'modifyTimestamp'
4. Directory Schema 20
4.1. Schema Definitions 21
4.1.1. Object Class Definitions 22
4.1.2. Attribute Types 23
4.1.3. Matching Rules 24
4.1.4. LDAP Syntaxes 25
4.1.5. DIT Content Rules 26
4.1.6. DIT Structural Rules and Name Forms 27
4.2. Subschema Subentries 29
4.2.1. 'objectClasses' 30
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4.2.2. 'attributeTypes'
4.2.3. 'matchingRules' 31
4.2.4. 'matchingRuleUse'
4.2.5. 'ldapSyntaxes'
4.2.6. 'dITContentRules' 32
4.2.7. 'dITStructureRules'
4.2.8. 'nameForms'
4.3. 'extensibleObject'
4.4. Subschema Discovery 33
5. DSA (Server) Informational Model
5.1. Server-specific Data Requirements 34
5.1.1. 'altServer' 35
5.1.2. 'namingContexts'
5.1.3. 'supportedControl'
5.1.4. 'supportedExtension' 36
5.1.5. 'supportedLDAPVersion'
5.1.6. 'supportedSASLMechanisms'
6. Other Considerations 37
6.1. Preservation of User Information
6.2. Short Names
6.3. Cache and Shadowing
7. Implementation Guidelines 38
7.1. Server Guidelines
7.2. Client Guidelines
8. Security Considerations 39
9. IANA Considerations
10. Acknowledgments 40
11. Author's Address
12. References
12.1. Normative References
12.2. Informative References 41
Appendix A. Changes 42
A.1 Changes to RFC 2251
A.1.1 Section 3.2 of RFC 2251
A.1.2 Section 3.4 of RFC 2251 43
A.1.2 Section 4 of RFC 2251
A.1.3 Section 6 of RFC 2251 44
A.2 Changes to RFC 2252
A.2.1 Section 4 of RFC 2252
A.2.2 Section 5 of RFC 2252
A.2.3 Section 7 of RFC 2252 45
A.3 Changes to RFC 2256
Copyright
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1. Introduction
This document discusses the X.500 Directory Information Models
[X.501], as used by the Lightweight Directory Access Protocol (LDAP)
[Roadmap].
The Directory is "a collection of open systems cooperating to provide
directory services" [X.500]. The information held in the Directory is
collectively known as the Directory Information Base (DIB). A
Directory user, which may be a human or other entity, accesses the
Directory through a client (or Directory User Agent (DUA)). The
client, on behalf of the directory user, interacts with one or more
servers (or Directory System Agents (DSA)). A server holds a fragment
of the DIB.
The DIB contains two classes of information:
1) user information (e.g., information provided and administrated
by users). Section 2 describes the Model of User Information.
2) administrative and operational information (e.g., information
used to administer and/or operate the directory). Section 3
describes the model of Directory Administrative and Operational
Information.
These two models, referred to as the generic Directory Information
Models, describe how information is represented in the Directory.
These generic models provide a framework for other information models.
Section 4 discusses the subschema information model and subschema
discovery. Section 5 discusses the DSA (Server) Informational Model.
Other X.500 information models, such as access control, collective
attribute, distribution knowledge, and replication knowledge
information models, may be adapted for use in LDAP. Specification of
how these models are to be used in LDAP is left to future documents.
1.1. Relationship to Other LDAP Specifications
This document is a integral part of the LDAP technical specification
[Roadmap] which obsoletes entirely the previously defined LDAP
technical specification [LDAPTS].
This document obsoletes RFC 2251 sections 3.2 and 3.4, as well as
portions of sections 4 and 6. Appendix A.1 summaries changes to these
sections. The remainder of RFC 2251 is obsoleted by the [Protocol],
[AuthMeth], and [Roadmap] documents.
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This document obsoletes RFC 2252 sections 4, 5 and 7. Appendix A.2
summaries changes to these sections. The remainder of RFC 2252 is
obsoleted by [Syntaxes] and [Schema].
This document obsoletes RFC 2256 sections 5.1, 5.2, 7.1 and 7.2.
Appendix A.3 summarizes changes to these sections. The remainder of
RFC 2256 is obsoleted by [Schema] and [Syntaxes].
1.2. Conventions
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].
Schema definitions are provided using LDAP description formats (as
defined in Section 4.1). Definitions provided here are formatted
(line wrapped) for readability. Matching rules and LDAP syntaxes
referenced in these defintions are defined in [Syntaxes].
1.3. Common ABNF Productions
A number of syntaxes in this document are described using ABNF
[RFC2234]. These syntaxes (as well as a number of syntaxes defined in
other documents) rely on the following common productions:
keystring = leadkeychar *keychar
leadkeychar = ALPHA
keychar = ALPHA / DIGIT / HYPHEN
number = DIGIT / ( LDIGIT 1*DIGIT )
ALPHA = %x41-5A / %x61-7A ; "A"-"Z" / "a"-"z"
DIGIT = %x30 / LDIGIT ; "0"-"9"
LDIGIT = %x31-39 ; "1"-"9"
HEX = DIGIT / %x41-46 / %x61-66 ; 0-9 / A-F / a-f
SP = 1*SPACE ; one or more " "
WSP = 0*SPACE ; zero or more " "
NULL = %x00 ; null (0)
SPACE = %x20 ; space (" ")
DQUOTE = %x22 ; quote (""")
SHARP = %x23 ; octothorpe (or sharp sign) ("#")
DOLLAR = %x24 ; dollar sign ("$")
SQUOTE = %x27 ; single quote ("'")
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LPAREN = %x28 ; left paren ("(")
RPAREN = %x29 ; right paren (")")
PLUS = %x2B ; plus sign ("+")
COMMA = %x2C ; comma (",")
HYPHEN = %x2D ; hypen ("-")
DOT = %x2E ; period (".")
SEMI = %x3B ; semicolon (";")
LANGLE = %x3C ; left angle bracket ("<")
EQUALS = %x3D ; equals sign ("=")
RANGLE = %x3E ; right angle bracket (">")
X = %x58 ; uppercase x ("X")
ESC = %x5C ; backslash ("\")
USCORE = %x5F ; underscore ("_")
LCURLY = %x7B ; left curly brace "{"
RCURLY = %x7D ; right curly brace "}"
; Any UTF-8 character
UTF8 = UTF1 / UTFMB
UTFMB = UTF2 / UTF3 / UTF4 / UTF5 / UTF6
UTF0 = %x80-BF
UTF1 = %x00-7F
UTF2 = %xC0-DF 1(UTF0)
UTF3 = %xE0-EF 2(UTF0)
UTF4 = %xF0-F7 3(UTF0)
UTF5 = %xF8-FB 4(UTF0)
UTF6 = %xFC-FD 5(UTF0)
; Any octet
OCTET = %x00-FF
Object identifiers are represented in LDAP using a dot-decimal format
conforming to the ABNF:
numericoid = number *( DOT number )
Short names, known as descriptors, are used as a more readable aliases
for object identifiers. Descriptors are case insensitive and conform
to the the ABNF:
descr = keystring
Where either an object identifier or a short name may be specified,
the following production is used:
oid = descr / numericoid
The <descr> form is preferred. When a production <oid> is encoded in
a value, the <descr> encoding option SHOULD be used instead of the
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<numericoid> encoding option.
2. Model of Directory User Information
As [X.501] states:
The purpose of the Directory is to hold, and provide access to,
information about objects of interest (objects) in some 'world'.
An object can be anything which is identifiable (can be named).
An object class is an identified family of objects, or conceivable
objects, which share certain characteristics. Every object belongs
to at least one class. An object class may be a subclass of other
object classes, in which case the members of the former class, the
subclass, are also considered to be members of the latter classes,
the superclasses. There may be subclasses of subclasses, etc., to
an arbitrary depth.
A directory entry, a named collection of information, is the basic
unit of information held in the Directory. An object entry represents
a particular object. An alias entry provides alternative naming. A
subentry holds administrative and/or operational information.
The set of entries representing the DIB are organized hierarchically
in a tree structure known as the Directory Information Tree (DIT).
Section 2.1 describes the Directory Information Tree
Section 2.2 discusses naming of entries.
Section 2.3 discusses the structure of entries.
Section 2.4 discusses object classes.
Section 2.5 discusses attributes
Section 2.6 discusses alias entries
2.1. The Directory Information Tree
As noted above, the DIB is composed of a set of entries organized
hierarchically in a tree structure known as the Directory Information
Tree (DIT). Specifically, a tree where vertices are the entries.
The arcs between vertices define relations between entries. If an arc
exists from X to Y, then the entry at X is the immediate superior of Y
and Y is the immediate subordinate of X. An entry's superiors is the
entry's immediate superior and its superiors. An entry's subordinates
is all of its immediate subordinates and their subordinates.
Similarly, the superior/subordinate relationship between object
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entries can be used to derive a relation between the objects they
represent. DIT structural rules can be used to govern relationships
between objects.
2.2. Naming of Entries
2.2.1. Relative Distinguished Names
Each entry is named relative to its immediate superior. This relative
name, known as its Relative Distinguished Name (RDN) [X.501], is
composed of one or more attribute value assertions (AVA) consisting of
an attribute description with zero options and an attribute value. An
entry's relative distinguished name must be unique among all its
siblings.
The following are example string representations of RDNs [LDAPDN]:
UID=12345
OU=Engineering
CN=Kurt Zeilenga+L=Redwood Shores
The last is an example of a multi-valued RDN.
2.2.2. Distinguished Names
An entry's fully qualified name, known as its Distinguished Name (DN)
[X.501], is the concatenation of its RDN and its immediate superior's
DN. A Distinguished Name unambiguously refers to an entry in the
tree. The following are example string representations of DNs
[LDAPDN]:
UID=nobody@example.com,DC=example,DC=com
CN=John Smith,OU=Sales,O=ACME Limited,L=Moab,ST=Utah,C=US
2.2.3. Alias Names
An alias, or alias name, is "an name for an object, provided by the
use of alias entries" [X.501]. Alias entries are described in Section
2.6.
2.3. Structure of an Entry
An entry consist of a set of attributes which hold information about
the object which entry represents.
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An attribute is an attribute description, a type and one or more
options, with one or more associated values. The attribute type
governs whether the attribute can have multiple values, the syntax and
matching rules used to construct and compare values of that attribute,
and other functions. Options indicate subtypes and other functions.
An example of an attribute is 'givenName' [Schema]. There can be one
or more values of this attribute, they must be directory strings, and
they are case insensitive (e.g. "John" will match "JOHN").
2.4. Object Classes
An object class is "an identified family of objects (or conceivable
objects) which share certain characteristics" [X.501].
As defined in [X.501]:
Object classes are used in the Directory for a number of purposes:
- describing and categorising objects and the entries that
correspond to these objects;
- where appropriate, controlling the operation of the Directory;
- regulating, in conjunction with DIT structure rule
specifications, the position of entries in the DIT;
- regulating, in conjunction with DIT content rule
specifications, the attributes that are contained in entries;
- identifying classes of entry that are to be associated with a
particular policy by the appropriate administrative authority.
An object class (a subclass) may be derived from an object class
(its direct superclass) which is itself derived from an even more
generic object class. For structural object classes, this process
stops at the most generic object class, 'top' (defined in Section
2.4.1). An ordered set of superclasses up to the most superior
object class of an object class is its superclass chain.
An object class may be derived from two or more direct
superclasses (superclasses not part of the same superclass chain).
This feature of subclassing is termed multiple inheritance.
Each object class identifies the set of attributes required to be
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present in entries belonging to the class and the set of attributes
allowed to be present in entries belonging to the class. As an entry
of a class must meet the requirements of each class it belongs to, it
can be said that an object class inherits the sets of allowed and
required attributes from its superclasses. A subclass can identify an
attribute allowed by a subclass as being required. If an attribute is
a member of both sets, it is required to be present.
Each object class is defined to be one of three kinds of object
classes: Abstract, Structural, and Auxiliary.
Each object is identified by an object identifier (OID) and,
optionally, one or more short names known as descriptors.
2.4.1. Abstract Object Classes
An Abstract object class, as the name implies, provides a base of
characteristics from which other object classes can be defined to
inherit from. An entry cannot belong to only abstract object classes.
Abstract object classes can not derive from structural nor auxiliary
object classes.
All structural object classes derive (directly or indirectly) from the
'top' abstract object class. Auxiliary object classes do not
necessarily derive from 'top'.
( 2.5.6.0 NAME 'top' ABSTRACT MUST objectClass )
All entries belong to the 'top' abstract class.
2.4.2. Structural Object Classes
As stated in [X.501]:
An object class defined for use in the structural specification of
the DIT is termed a structural object class. Structural object
classes are used in the definition of the structure of the names
of the objects for compliant entries.
An object or alias entry is characterised by precisely one
structural object class superclass chain which has a single
structural object class as the most subordinate object class.
This structural object class is referred to as the structural
object class of the entry.
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Structural object classes are related to associated entries:
- an entry conforming to a structural object class shall
represent the real-world object constrained by the object
class;
- DIT structure rules only refer to structural object classes;
the structural object class of an entry is used to specify the
position of the entry in the DIT;
- the structural object class of an entry is used, along with an
associated DIT content rule, to control the content of an
entry.
The structural object class of an entry shall not be changed.
Each structural object class is a (direct or indirect) subclass of the
'top' abstract object class.
Structural object classes cannot subclass auxiliary object classes.
Each entry is said to belong to its structural object class as well as
all classes in its structural object class's superclass chain, which
always includes 'top'.
2.4.3. Auxiliary Object Classes
Auxiliary object classes are used augment the characteristics of
entries. They are commonly used to augment the sets of attributes
required and allowed attributes to be present in an entry. They can
be used to describe entries or classes of entries.
Auxiliary object classes cannot subclass structural object classes.
Each entry can belong to any number of auxiliary object classes. The
set of auxiliary object classes which an entry belongs to can change
over time.
2.5. Attribute Descriptions
An attribute description is composed of an attribute type (see Section
2.5.1) and a set of zero or more attribute options (see Section
2.5.2).
An attribute description is represented by the ABNF:
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attributedescription = attributetype options
attributetype = oid
options = *( SEMI option )
option = 1*keychar
where <attributetype> identifies the attribute type and each <option>
identifies an attribute option. Both <attributetype> and <option>
productions are case insensitive. The order in which <option>s appear
is irrelevant. That is, any two <attributedescription>s which consist
of the same <attributetype> and same set of <option>s are equivalent.
Examples of valid attribute descriptions:
2.5.4.0
cn;lang-de;lang-en
owner
An attribute description which consisting of an unrecognized attribute
type is to be treated as unrecongized. Servers SHALL treat an
attribute description with an unrecognized attribute option as
unrecongized. Client MAY treat an unrecongized attribute option as a
tagging option (see Section 2.5.2.1).
All attributes of an entry must have distinct attribute descriptions.
2.5.1. Attribute Types
An attribute type governs whether the attribute can have multiple
values, the syntax and matching rules used to construct and compare
values of that attribute, and other functions.
A user attribute type has userApplications usage. An operational
attribute type has one of three usages: directoryOperation,
distributedOperation, or dsaOperation. An operational attribute type
may be defined as not modifiable by users.
A user attribute type cannot be a subtype of an operational attribute
type. An operational attribute type which is a subtype must be
subtype of an operational attribute type of the same usage
(application).
An attribute type (a subtype) may derive from another attribute type
(a direct supertype). The subtype inherits the matching rules and
syntax of its supertype.
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An attribute description consisting of a subtype and no options is
said to the direct description subtype of the attribute description
consisting of the subtype's direct supertype and no options.
Each attribute type is identified by an object identifier (OID) and,
optionally, one or more short names known as descriptors.
Procedures for registering descriptors are detailed in [LDAPIANA].
2.5.2. Attribute Options
There are multiple kinds of attribute description options. The LDAP
technical specification details one kind: tagging options.
Not all options can be associated with attributes held in the
directory. Tagging options can be.
Not all options can be use in conjunction with all attribute types.
In such cases, the attribute description is to be treated as
unrecognized.
An attribute description that contains mutually exclusive options
shall be treated as unrecognized. That is, "cn;x-bar;x-foo" (where
"x-foo" and "x-bar" are mutually exclusive) is to be treated as
unrecognized.
Other kinds of options may be specified in future documents. These
documents must detail how new kinds of options they define relate to
tagging and transfer options. In particular, these documents must
detail whether or not new kinds of options can be associated with
attributes held in the directory, how new kinds of options affect
transfer of attribute values, and how new kinds of options are treated
in attribute description hierarchies.
Options are represented as short case insensitive textual strings
conforming to the <option> production defined in Section 2.5 of this
document.
Procedures for registering options are detailed in [LDAPIANA].
2.5.2.1. Tagging Options
Attributes held in the directory can have attribute descriptions with
one or more tagging options. Tagging options are never mutually
exclusive.
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An attribute description with N tagging options is consider a direct
(description) subtype of all attribute descriptions of the same
attribute type and all but one of the N options. If the attribute
type has a supertype, then the attribute description is also
considered a direct (description) subtype of the attribute description
of the supertype and the N tagging options. That is,
'cn;lang-de;lang-en' is considered a direct subtype of 'cn;lang-de',
'cn;lang-en', and 'name;lang-de;lang-en' ('cn' is a subtype of 'name',
both are defined in [Schema]).
2.5.3. Attribute Description Hierarchies
An attribute description can be the direct subtype of zero or more
other attribute descriptions as indicated by attribute type subtyping
(as described in Section 2.5.1) or attribute tagging option subtyping
(as described in Section 2.5.2.1). These subtyping relationships are
used to form hierarchies of attribute descriptions and attributes.
As adapted from [X.501]:
Attribute hierarchies allow access to the DIB with varying degrees
of granularity. This is achieved by allowing the value components
of attributes to be accessed by using either their specific
attribute description (a direct reference to the attribute) or by
a more generic attribute description (an indirect reference).
Semantically related attributes may be placed in a hierarchical
relationship, the more specialized being placed subordinate to the
more generalized. Searching for, or retrieving attributes and
their values is made easier by quoting the more generalized
attribute description; a filter item so specified is evaluated for
the more specialized descriptions as well as for the quoted
description.
Where subordinate specialized descriptions are selected to be
returned as part of a search result these descriptions shall be
returned if available. Where the more general descriptions are
selected to be returned as part of a search result both the
general and the specialized descriptions shall be returned, if
available. An attribute value shall always be returned as a value
of its own attribute description.
All of the attribute descriptions in an attribute hierarchy are
treated as distinct and unrelated descriptions for the purpose of
administration of the entry and for user modification of entry
content.
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For an entry to contain a value of an attribute description
belonging to an attribute hierarchy, the attribute type of that
description must be explicitly included either in the definition
of an object class to which the entry belongs, or because the DIT
content rule applicable to that entry permits it.
An attribute value stored in a object or alias entry is of
precisely one attribute description. The description is indicated
when the value is originally added to the entry.
The indicated description may include options not stored with as part
of the attribute.
2.5.4. Attribute Values
Attribute values conform to the defined syntax of the attribute.
When an attribute is used for naming of the entry, one and only one
value of the attribute is selected to appear in the Relative
Distinguished Name. This value is known as a distinguished value.
Only attributes whose descriptions have no options can be used for
naming.
2.6. Alias Entries
As adapted from [X.501]:
An alias, or an alias name, for an object is a an alternative name
for an object or object entry which is provided by the use of
alias entries.
Each alias entry contains, within the 'aliasedObjectName'
attribute (known as the 'aliasedEntryName' attribute in X.500]), a
name of some object. The distinguished name of the alias entry is
thus also a name for this object.
NOTE - The name within the 'aliasedObjectName' is said to be
pointed to by the alias. It does not have to be the
distinguished name of any entry.
The conversion of an alias name to an object name is termed
(alias) dereferencing and comprises the systematic replacement of
alias names, where found within a purported name, by the value of
the corresponding 'aliasedObjectName' attribute. The process may
require the examination of more than one alias entry.
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Any particular entry in the DIT may have zero or more alias names.
It therefore follows that several alias entries may point to the
same entry. An alias entry may point to an entry that is not a
leaf entry and may point to another alias entry.
An alias entry shall have no subordinates, so that an alias entry
is always a leaf entry.
Every alias entry shall belong to the 'alias' object class.
2.6.1. 'alias' object class
Alias entries belong to the 'alias' object class.
( 2.5.6.1 NAME 'alias' SUP top STRUCTURAL MUST aliasedObjectName )
2.6.2. 'aliasedObjectName' attribute type
The 'aliasedObjectName' attribute holds the name of the entry an alias
points to. The 'aliasedObjectName' attribute is known as the
'aliasedEntryName' attribute in X.500.
( 2.5.4.1 NAME 'aliasedObjectName' EQUALITY distinguishedNameMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.12 SINGLE-VALUE )
The 'distinguishedNameMatch' matching rule and the DistinguishedName
(1.3.6.1.4.1.1466.115.121.1.12) syntax is defined in [Syntaxes].
3. Directory Administrative and Operational Information
This section discusses select aspects of the X.500 Directory
Administrative and Operational Information model [X.501]. LDAP
implementations MAY support other aspects of this model.
3.1. Subtrees
As defined in [X.501]:
A subtree is a collection of object and alias entries situated at
the vertices of a tree. Subtrees do not contain subentries. The
prefix sub, in subtree, emphasizes that the base (or root) vertex
of this tree is usually subordinate to the root of the DIT.
A subtree begins at some vertex and extends to some identifiable
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lower boundary, possibly extending to leaves. A subtree is always
defined within a context which implicitly bounds the subtree. For
example, the vertex and lower boundaries of a subtree defining a
replicated area are bounded by a naming context. Similarly, the
scope of a subtree defining a specific administrative area is
limited to the context of an enclosing autonomous administrative
area.
3.2. Subentries
A subentry is a "special sort of entry, known by the Directory, used
to hold information associated with a subtree or subtree refinement"
[X.501]. Subentries are used in Directory to hold for administrative
and operational purposes as defined in [X.501]. Their use in LDAP is
not detailed in this technical specification, but may be detailed in
future documents.
The term "(sub)entry" in this specification indicates that servers
implementing X.500(93) models are to use a subentry and other servers
use an object entry belonging to the appropriate auxiliary class
normally used with the subentry (e.g., 'subschema' for subschema
subentries) to mimic the subentry. This object entry's RDN SHALL be
formed from a value of the 'cn' (commonName) attribute [Schema].
3.3. The 'objectClass' attribute
Each entry in the DIT has an 'objectClass' attribute.
( 2.5.4.0 NAME 'objectClass'
EQUALITY objectIdentifierMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.38 )
The 'objectIdentifierMatch' matching rule and OBJECT IDENTIFIER
(1.3.6.1.4.1.1466.115.121.1.38) syntax is defined in [Syntaxes].
The 'objectClass' attribute specifies the object classes of an entry,
which (among other things) is used in conjunction with user and system
schema to determine the permitted attributes of an entry. Values of
this attribute can be modified by clients, but the 'objectClass'
attribute cannot be removed.
Servers which follow X.500(93) models SHALL restrict modifications of
this attribute to prevent the basic structural class of the entry from
being changed (e.g. one cannot change a 'person' into a 'country').
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When creating an entry or adding an 'objectClass' value to an entry,
all superclasses of the named classes are implicitly added as well if
not already present, and the client must supply values for any
mandatory attributes of new superclasses.
3.4. Operational attributes
Some attributes, termed operational attributes (as defined in Section
12.4.1 of [X.501]), are used or maintained by servers for
administrative and operational purposes. Not all operational
attributes are user modifiable.
Operational attributes are not normally visible. They are not
returned in search results unless explicitly requested by name.
Entries may contain, among others, the following operational
attributes.
- creatorsName: the Distinguished Name of the user who added this
entry to the directory.
- createTimestamp: the time this entry was added to the directory.
- modifiersName: the Distinguished Name of the user who last
modified this entry.
- modifyTimestamp: the time this entry was last modified.
Servers SHOULD maintain the 'creatorsName', 'createTimestamp',
'modifiersName', and 'modifyTimestamp' for all entries of the DIT.
3.4.1. 'creatorsName'
This attribute appears in entries which were added using the protocol
(e.g., using the Add operation). The value is the distinguised name
of the creator.
( 2.5.18.3 NAME 'creatorsName'
EQUALITY distinguishedNameMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.12
SINGLE-VALUE NO-USER-MODIFICATION
USAGE directoryOperation )
The 'distinguishedNameMatch' matching rule and the DistinguishedName
(1.3.6.1.4.1.1466.115.121.1.12) syntax are defined in [Syntaxes].
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3.4.2. 'createTimestamp'
This attribute appears in entries which were added using the protocol
(e.g., using the Add operation). The value is the time the entry was
added.
( 2.5.18.1 NAME 'createTimestamp'
EQUALITY generalizedTimeMatch
ORDERING generalizedTimeOrderingMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.24
SINGLE-VALUE NO-USER-MODIFICATION
USAGE directoryOperation )
The 'generalizedTimeMatch' and 'generalizedTimeOrderingMatch' matching
rules and the GeneralizedTime (1.3.6.1.4.1.1466.115.121.1.24) syntax
are defined in [Syntaxes].
3.4.3. 'modifiersName'
This attribute appears in entries which have been modified using the
protocol (e.g., using Modify operation). The value is the
distinguised name of the last modifier.
( 2.5.18.4 NAME 'modifiersName'
EQUALITY distinguishedNameMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.12
SINGLE-VALUE NO-USER-MODIFICATION
USAGE directoryOperation )
The 'distinguishedNameMatch' matching rule and the DistinguishedName
(1.3.6.1.4.1.1466.115.121.1.12) syntax are defined in [Syntaxes].
3.4.4. 'modifyTimestamp'
This attribute appears in entries which have been modified using the
protocol (e.g., using the Modify operation). The value is the time
the entry was last modified.
( 2.5.18.2 NAME 'modifyTimestamp'
EQUALITY generalizedTimeMatch
ORDERING generalizedTimeOrderingMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.24
SINGLE-VALUE NO-USER-MODIFICATION
USAGE directoryOperation )
The 'generalizedTimeMatch' and 'generalizedTimeOrderingMatch' matching
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rules and the GeneralizedTime (1.3.6.1.4.1.1466.115.121.1.24) syntax
are defined in [Syntaxes].
4. Directory Schema
As defined in [X.501]:
The Directory Schema is a set of definitions and constraints
concerning the structure of the DIT, the possible ways entries are
named, the information that can be held in an entry, the
attributes used to represent that information and their
organization into hierarchies to facilitate search and retrieval
of the information and the ways in which values of attributes may
be matched in attribute value and matching rule assertions.
NOTE 1 - The schema enables the Directory system to, for example:
- prevent the creation of subordinate entries of the wrong
object-class (e.g. a country as a subordinate of a person);
- prevent the addition of attribute-types to an entry
inappropriate to the object-class (e.g. a serial number to a
person's entry);
- prevent the addition of an attribute value of a syntax not
matching that defined for the attribute-type (e.g. a printable
string to a bit string).
Formally, the Directory Schema comprises a set of:
a) Name Form definitions that define primitive naming relations
for structural object classes;
b) DIT Structure Rule definitions that define the names that
entries may have and the ways in which the the entries may be
related to one another in the DIT;
c) DIT Content Rule definitions that extend the specification of
allowable attributes for entries beyond those indicated by the
structural object classes of the entries;
d) Object Class definitions that define the basic set of mandatory
and optional attributes that shall be present, and may be
present, respectively, in an entry of a given class, and which
indicate the kind of object class that is being defined;
e) Attribute Type definitions that identify the object identifier
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by which an attribute is known, its syntax, associated matching
rules, whether it is an operational attribute and if so its
type, whether it is a collective attribute, whether it is
permitted to have multiple values and whether or not it is
derived from another attribute type;
f) Matching Rule definitions that define matching rules.
And in LDAP:
g) LDAP Syntaxes definitions that define encodings used in LDAP.
4.1. Schema Definitions
Schema definitions in this section are described using ABNF and rely
on the common productions specified in Section 1.2 as well as these:
noidlen = numericoid [ LCURLY len RCURLY ]
len = number
oids = oid / ( LPAREN SP oidlist SP RPAREN )
oidlist = oid *( SP DOLLAR SP oid )
extensions = *( SP xstring SP qdstrings )
xstring = X HYPHEN 1*( ALPHA / HYPHEN / USCORE )
qdescrs = qdescr / ( LPAREN WHSP qdescrlist WHSP RPAREN )
qdescrlist = [ qdescr *( WHSP qdescr ) ]
qdescr = SQUOTE descr SQUOTE
qdstring = SQUOTE dstring SQUOTE
dstring = 1*( QS / QQ / QUTF8 ) ; escaped UTF8 string
QQ = ESC %x32 %x37 ; "\27"
QS = ESC %x35 ( %x43 / %x63 ) ; "\5C" / "\5C"
; Any UTF-8 encoded UCS character
; except %x27 ("'") and %x5C ("\")
QUTF8 = QUTF1 / UTFMB
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; Any ASCII character except %x27 ("'") and %x5C ("\")
QUTF1 = %x00-26 / %x28-5B / %x5D-7F
Schema definitions in this section also share a number of common
terms.
The NAME field provides a set of short names (descriptors) which are
be used as aliases for the OID.
The DESC field optionally allows a descriptive string to be provided
by the directory administrator and/or implementor. While
specifications may suggest a descriptive string, there is no
requirement that the suggested (or any) descriptive string be used.
Implementors should note that future versions of this document may
expand these definitions to include additional terms. Terms whose
identifier begins with "X-" are reserved for private experiments, and
MUST be followed by a <space> and a <qdstrings> tokens.
4.1.1. Object Class Definitions
Object Class definitions are written according to the ABNF:
ObjectClassDescription = RPAREN WSP
numericoid ; object identifer
[ SP "NAME" SP qdescrs ] ; short names
[ SP "DESC" SP qdstring ] ; description
[ SP "OBSOLETE" ] ; not active
[ SP "SUP" SP oids ] ; superior object classes
[ SP kind ] ; kind of class
[ SP "MUST" SP oids ] ; attribute types
[ SP "MAY" SP oids ] ; attribute types
extensions WSP RPAREN
kind = "ABSTRACT" / "STRUCTURAL" / "AUXILIARY"
where:
<numericoid> is object identifier assigned to this object class;
NAME <qdescrs> are short names identifying this object class;
DESC <qdstring> is a store descriptive string;
OBSOLETE indicates this object class is not active;
SUP <oids> specifies the direct superclasses of this object class;
the kind of object class is indicated by one of ABSTRACT,
STRUCTURAL, or AUXILIARY, default is STRUCTURAL;
MUST and MAY specify the sets of required and allowed attribute
types, respectively; and
<extensions> describe extensions.
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4.1.2. Attribute Types
Attribute Type definitions are written according to the ABNF:
AttributeTypeDescription = LPAREN WSP
numericoid ; object identifer
[ SP "NAME" SP qdescrs ] ; short names
[ SP "DESC" SP qdstring ] ; description
[ SP "OBSOLETE" ] ; not active
[ SP "SUP" SP oid ] ; subtype
[ SP "EQUALITY" SP oid ] ; equality matching rule
[ SP "ORDERING" SP oid ] ; ordering matching rule
[ SP "SUBSTR" SP oid ] ; substrings matching rule
[ SP "SYNTAX" SP noidlen ] ; value syntax
[ SP "SINGLE-VALUE" ] ; single-value
[ SP "COLLECTIVE" ] ; collective
[ SP "NO-USER-MODIFICATION" ] ; not user modifiable
[ SP "USAGE" SP usage ] ; usage
extensions WSP RPAREN ; extensions
usage = "userApplications" /
"directoryOperation" /
"distributedOperation" / ; DSA-shared
"dsaOperation" ; DSA-specific
where:
<numericoid> is object identifier assigned to this attribute type;
NAME <qdescrs> are short names identifying this attribute type;
DESC <qdstring> is a store descriptive string;
OBSOLETE indicates this attribute type is not active;
SUP oid specifies the direct subtype of this type;
EQUALITY, ORDERING, SUBSTRING provide the oid of the equality,
ordering, and substrings matching rules, respectively;
SYNTAX identifies value syntax by object identifier and suggests a
minimum upper bound;
COLLECTIVE indicates this attribute type is collective;
NO-USER-MODIFICATION indicates this attribute type is not user
modifiable;
USAGE indicates the application of this attribute type; and
<extensions> describe extensions.
Each attribute type description must contain at least one of the SUP
or SYNTAX fields.
The default USAGE is userApplications. COLLECTIVE requires USAGE
userApplications. NO-USER_MODIFICATION requires usage other than
userApplications.
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Note that the <AttributeTypeDescription> does not list the matching
rules which can can be used with that attribute type in an
extensibleMatch search filter. This is done using the
'matchingRuleUse' attribute described in Section 4.1.3.
This document refines the schema description of X.501 by requiring
that the SYNTAX field in an <AttributeTypeDescription> be a string
representation of an object identifier for the LDAP string syntax
definition with an optional indication of the suggested minimun bound
of a value of this attribute.
A suggested minimum upper bound on the number of characters in a value
with a string-based syntax, or the number of bytes in a value for all
other syntaxes, may be indicated by appending this bound count inside
of curly braces following the syntax's OBJECT IDENTIFIER in an
Attribute Type Description. This bound is not part of the syntax name
itself. For instance, "1.3.6.4.1.1466.0{64}" suggests that server
implementations should allow a string to be 64 characters long,
although they may allow longer strings. Note that a single character
of the Directory String syntax may be encoded in more than one octet
since UTF-8 is a variable-length encoding.
4.1.3. Matching Rules
Matching rules are used by servers to compare attribute values against
assertion values when performing Search and Compare operations. They
are also used to identify the value to be added or deleted when
modifying entries, and are used when comparing a purported
distinguished name with the name of an entry.
A matching rule specifes the syntax of the assertion value.
Each matching rule is identified by an object identifier (OID) and,
optionally, one or more short names known as descriptors.
Matching rule definitions are written according to the ABNF:
MatchingRuleDescription = LPAREN WSP
numericoid ; object identifer
[ SP "NAME" SP qdescrs ] ; short names
[ SP "DESC" SP qdstring ] ; description
[ SP "OBSOLETE" ] ; not active
SP "SYNTAX" SP numericoid ; oid corrected to numericoid
extensions WSP RPAREN ; extensions
where:
<numericoid> is object identifier assigned to this matching rule;
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NAME <qdescrs> are short names identifying this matching rule;
DESC <qdstring> is a store descriptive string;
OBSOLETE indicates this matching rule is not active;
SYNTAX identifies the assertion syntax by object identifier; and
<extensions> describe extensions.
A matching rule use lists the attributes which are suitable for use
with an extensible matching rule.
Matching rule use descriptions (see Section 4.1.3) are written
according to the following ABNF:
MatchingRuleUseDescription = LPAREN WSP
numericoid ; object identifer
[ SP "NAME" SP qdescrs ] ; short names
[ SP "DESC" SP qdstring ] ; description
[ SP "OBSOLETE" ] ; not active
SP "APPLIES" SP oids ; attribute types
extensions WSP RPAREN ; extensions
where:
<numericoid> is the object identifier of the matching rule
associated with this matching rule use description;
NAME <qdescrs> are short names identifying this matching rule use;
DESC <qdstring> is a store descriptive string;
OBSOLETE indicates this matching rule use is not active;
APPLIES provides a list of attribute types the matching rule applies
to; and
<extensions> describe extensions.
4.1.4. LDAP Syntaxes
LDAP Syntaxes of (attribute and assertion) values are described in
terms of ASN.1 [X.680] and, optionally, have an octet string encoding
known as the LDAP-specific encoding. Commonly, the LDAP-specific
encoding is constrained to string of Universal Character Set (UCS)
[ISO10646] characters in UTF-8 [RFC2279] form.
Each LDAP syntax is identified by an object identifier (OID). These
are not intended to be displayed to users.
LDAP syntax definitions are written according to the ABNF:
SyntaxDescription = LPAREN WSP
numericoid ; object identifer
[ SP "DESC" SP qdstring ] ; description
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extensions WSP RPAREN ; extensions
where:
<numericoid> is object identifier assigned to this LDAP syntax;
DESC <qdstring> is a store descriptive string; and
<extensions> describe extensions.
4.1.5. DIT Content Rules
A DIT content rule is a "rule governing the content of entries of a
particular structural object class" [X.501].
A DIT content rule specifies for DIT entries of a particular
structural object class, which auxiliary object classes the entries
are allowed to belong to and which additional attributes (by type) are
required, allowed or not allowed to appear in the entries.
The list of precluded attributes cannot include any attribute listed
as mandatory in rule, the structural object class, or any of the
allowed auxiliary object classes.
Each content rule is identified by the object identifer, as well as
any short names, of the structural rule it applies to.
An entry may only belong to auxiliary object classes listed in the
governing content rule.
An entry must contain all attributes required by the object classes
the entry belongs to as well as all attributed required by the
governing content rule.
An entry may contain any non-precluded attributes allowed by the
object classes the entry belongs to as well as all attributes allowed
by the governing content rule.
An entry cannot include any attribute precluded by the governing
content rule.
An entry is governed by (if present and active in the subschema) the
DIT content rule which applies to the structural object class of the
entry (see Section 2.4.2). If no active rule is present for the
entry's structural object class, the entry's content is governed by
the structural object class (and possibly other aspects of user and
system schema).
DIT content rule descriptions are written according to the ABNF:
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DITContentRuleDescription = LPAREN WSP
numericoid ; object identifer
[ SP "NAME" SP qdescrs ] ; short names
[ SP "DESC" SP qdstring ] ; description
[ SP "OBSOLETE" ] ; not active
[ SP "AUX" SP oids ] ; auxiliary object classes
[ SP "MUST" SP oids ] ; attribute types
[ SP "MAY" SP oids ] ; attribute types
[ SP "NOT" SP oids ] ; attribute types
extensions WSP RPAREN ; extensions
where:
<numericoid> is the object identifier of the structural object class
associated with this DIT content rule;
NAME <qdescrs> are short names identifying this DIT content rule;
DESC <qdstring> is a store descriptive string;
OBSOLETE indicates this DIT content rule use is not active;
AUX specifies a list of auxiliary object classes which entries
subject to this DIT content rule may belong to;
MUST, MAY, and NOT specify lists of attribute types which are
required, allowed, or precluded, respectively, from appearing in
entries subject to this DIT content rule; and
<extensions> describe extensions.
4.1.6. DIT Structural Rules and Name Forms
It is sometimes desirable to regulate where object entries can be
placed in the DIT and how they can be named based upon their
structural object class.
A DIT structural rule is a "rule governing the structure of the DIT by
specifying a permitted superior to subordinate entry relationship. A
structure rule relates a name form, and therefore a structural object
class, to superior structure rules. This permits entries of the
structural object class identified by the name form to exist in the
DIT as subordinates to entries governed by the indicated superior
structure rules" [X.501].
A name form "specifies a permissible RDN for entries of a particular
structural object class. A name form identifies a named object class
and one or more attribute types to be used for naming (i.e. for the
RDN). Name forms are primitive pieces of specification used in the
definition of DIT structure rules" [X.501].
Each name form indicates the structural object class to be named, a
set of required attribute types, and a set of allowed attributes
types. A particular attribute type cannot be listed in both sets.
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Entries governed by the form must be named using a value from each
required attribute type and zero or more values from the allowed
attribute types.
Each name form is identified by an object identifier (OID) and,
optionally, one or more short names known as descriptors.
DIT structure rule descriptions are written according to the ABNF:
DITStructureRuleDescription = LPAREN WSP
ruleid ; rule identifier
[ SP "NAME" SP qdescrs ] ; short names
[ SP "DESC" SP qdstring ] ; description
[ SP "OBSOLETE" ] ; not active
SP "FORM" SP oid ; NameForm
[ SP "SUP" ruleids ] ; superior rules
extensions WSP RPAREN ; extensions
ruleids = ruleid / LPAREN WSP ruleidlist WSP RPAREN
ruleidlist = [ ruleid *( SP ruleid ) ]
ruleid = number
where:
<ruleid> is the rule identifier of this DIT structure rule;
NAME <qdescrs> are short names identifying this DIT structure rule;
DESC <qdstring> is a store descriptive string;
OBSOLETE indicates this DIT structure rule use is not active;
FORM is specifies the name form associated with this DIT strucure
rule;
SUP identifies superior rules (by rule id); and
<extensions> describe extensions.
Name form descriptions are written according to the ABNF:
NameFormDescription = LPAREN WSP
numericoid ; object identifer
[ SP "NAME" SP qdescrs ] ; short names
[ SP "DESC" SP qdstring ] ; description
[ SP "OBSOLETE" ] ; not active
SP "OC" SP oid ; structural object class
SP "MUST" SP oids ; attribute types
[ SP "MAY" SP oids ] ; attribute types
extensions WSP RPAREN ; extensions
where:
<numericoid> is object identifier assigned to this name form;
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NAME <qdescrs> are short names identifying this name form;
DESC <qdstring> is a store descriptive string;
OBSOLETE indicates this name form is not active;
OC identifies the structural object class this rule applies to,
MUST and MAY specify the sets of required and allowed, respectively,
naming attributes for this name form; and
<extensions> describe extensions.
4.2. Subschema Subentries
Subschema (sub)entries are used for administering information about
the directory schema. A single subschema (sub)entry contains all
schema definitions (see Section 4.1) used by entries in a particular
part of the directory tree.
Servers which follow X.500(93) models SHOULD implement subschema using
the X.500 subschema mechanisms (as detailed in Section 12 of [X.501]),
and so these are not ordinary object entries but subentries (see
Section 3.2). LDAP clients SHOULD NOT assume that servers implement
any of the other aspects of X.500 subschema.
Servers MAY allow modification of subschema. Procedures for Subschema
Modification are discussed in Section 14.5 of [X.501].
A server which masters entries and permits clients to modify these
entries MUST implement and provide access to these subschema
(sub)entries including providing a 'subschemaSubentry' attribute in
each modifiable entry. This so clients may discover the attributes
and object classes which are permitted to be present. It is strongly
RECOMMENDED that all other servers implement this as well.
A server SHALL only publish schema definitions for elements it
supports. It is noted that servers do not necessarily have to support
all schema elements referenced by a published definition.
The value of the 'subschemaSubentry' attribute is the name of the
subschema (sub)entry holding the subschema controlling the entry.
( 2.5.18.10 NAME 'subschemaSubentry'
EQUALITY distinguishedNameMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.12
NO-USER-MODIFICATION SINGLE-VALUE
USAGE directoryOperation )
The 'distinguishedNameMatch' matching rule and the DistinguishedName
(1.3.6.1.4.1.1466.115.121.1.12) syntax are defined in [Syntaxes].
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Subschema is held in (sub)entries belonging to the subschema auxiliary
object class.
( 2.5.20.1 NAME 'subschema' AUXILIARY
MAY ( dITStructureRules $ nameForms $ ditContentRules $
objectClasses $ attributeTypes $ matchingRules $
matchingRuleUse ) )
The 'ldapSyntaxes' operational attribute may also be present in
subschema entries.
Servers MAY provide other attributes in subschema (sub)entries to
reflect additional supported capabilities or for other administrative
and operational purposes.
Servers SHOULD provide the attributes 'createTimestamp' and
'modifyTimestamp' in subschema (sub)entries, in order to allow clients
to maintain their caches of schema information.
The following subsections provide attribute type definitions for each
of schema definition attribute types.
4.2.1. 'objectClasses'
This attribute holds definitions of object classes supported in the
subschema.
( 2.5.21.6 NAME 'objectClasses'
EQUALITY objectIdentifierFirstComponentMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.37
USAGE directoryOperation )
The 'objectIdentifierFirstComponentMatch' matching rule and the
ObjectClassDescription (1.3.6.1.4.1.1466.115.121.1.37) syntax are
defined in [Syntaxes].
4.2.2. 'attributeTypes'
This attribute holds definitions of attribute types supported in the
subschema.
( 2.5.21.5 NAME 'attributeTypes'
EQUALITY objectIdentifierFirstComponentMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.3
USAGE directoryOperation )
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The 'objectIdentifierFirstComponentMatch' matching rule and the
AttributeTypeDescription (1.3.6.1.4.1.1466.115.121.1.3) syntax are
defined in [Syntaxes].
4.2.3. 'matchingRules'
This attribute holds definitions of matching rules supported in the
subschema.
( 2.5.21.4 NAME 'matchingRules'
EQUALITY objectIdentifierFirstComponentMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.30
USAGE directoryOperation )
The 'objectIdentifierFirstComponentMatch' matching rule and the
MatchingRuleDescription (1.3.6.1.4.1.1466.115.121.1.30) syntax are
defined in [Syntaxes].
4.2.4 'matchingRuleUse'
This attribute holds definitions of matching rule uses supported in
the subschema.
( 2.5.21.8 NAME 'matchingRuleUse'
EQUALITY objectIdentifierFirstComponentMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.31
USAGE directoryOperation )
The 'objectIdentifierFirstComponentMatch' matching rule and the
MatchingRuleUseDescription (1.3.6.1.4.1.1466.115.121.1.31) syntax are
defined in [Syntaxes].
4.2.5. 'ldapSyntaxes'
This attribute holds definitions of LDAP syntaxes supported in the
subschema.
( 1.3.6.1.4.1.1466.101.120.16 NAME 'ldapSyntaxes'
EQUALITY objectIdentifierFirstComponentMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.54
USAGE directoryOperation )
The 'objectIdentifierFirstComponentMatch' matching rule and the
SyntaxDescription (1.3.6.1.4.1.1466.115.121.1.54) syntax are defined
in [Syntaxes].
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4.2.6. 'dITContentRules'
This attribute lists DIT Content Rules which are in force.
( 2.5.21.2 NAME 'dITContentRules'
EQUALITY objectIdentifierFirstComponentMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.16
USAGE directoryOperation )
The 'objectIdentifierFirstComponentMatch' matching rule and the
DITContentRuleDescription (1.3.6.1.4.1.1466.115.121.1.16) syntax are
defined in [Syntaxes].
4.2.7. 'dITStructureRules'
This attribute lists DIT Structure Rules which are in force.
( 2.5.21.1 NAME 'dITStructureRules'
EQUALITY integerFirstComponentMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.17
USAGE directoryOperation )
The 'integerFirstComponentMatch' matching rule and the
DITStructureRuleDescription (1.3.6.1.4.1.1466.115.121.1.17) syntax are
defined in [Syntaxes].
4.2.8 'nameForms'
This attribute lists Name Forms which are in force.
( 2.5.21.7 NAME 'nameForms'
EQUALITY objectIdentifierFirstComponentMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.35
USAGE directoryOperation )
The 'objectIdentifierFirstComponentMatch' matching rule and the
NameFormDescription (1.3.6.1.4.1.1466.115.121.1.35) syntax are defined
in [Syntaxes].
4.3. 'extensibleObject' object class
The 'extensibleObject auxiliary object class allows entries belong to
it to hold any attribute type. The set of allowed attributes of this
class is implicitly the set of all user attributes.
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( 1.3.6.1.4.1.1466.101.120.111 NAME 'extensibleObject'
SUP top AUXILIARY )
The mandatory attributes of the other object classes of this entry are
still required to be present and any precluded attributes are still
not allowed to be present.
Note that not all servers will implement this object class, and those
which do not will reject requests to add entries which contain this
object class, or modify an entry to add this object class.
4.4. Subschema Discovery
To discover the DN of the subschema (sub)entry holding the subschema
controlling a particular entry (or subentry), a client reads that
entry's 'subschemaSubentry' operational attribute. To read schema
attributes from the subschema (sub)entry, clients MUST issue a base
object search where the filter is "(objectClass=subschema)" and the
list of attributes includes the names of the desired schema attributes
(as they are operational). This filter allows LDAP servers which
gateway to X.500 to detect that subentry information is being
requested.
Clients SHOULD NOT assume that server supports all referenced elements
of a particular definition. For example, a client is not to assume
the server supports the EQUALITY matching rule of a listed attribute
unless the server publishes a definition for that matching rule.
5. DSA (Server) Informational Model
The LDAP protocol assumes there are one or more servers which jointly
provide access to a Directory Information Tree (DIT).
As defined in [X.501]:
context prefix: The sequence of RDNs leading from the Root of the
DIT to the initial vertex of a naming context; corresponds to
the distinguished name of that vertex.
DIB fragment: The portion of the DIB that is held by one master
DSA, comprising one or more naming contexts.
naming context: A subtree of entries held in a single master DSA.
That is, a naming context is the largest collection of entries,
starting at an entry that is mastered by a particular server, and
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including all its subordinates and their subordinates, down to the
entries which are mastered by different servers. And the context
prefix is the name of the initial entry.
The root of the DIT is a DSA-specific Entry (DSE) and not part of any
naming context (or any subtree); each server has different attribute
values in the root DSE.
5.1. Server-specific Data Requirements
An LDAP server MUST provide information about itself and other
information that is specific to each server. This is represented as a
group of attributes located in the root DSE (DSA-Specific Entry),
which is named with the zero-length LDAPDN. These attributes are
retrievable, subject to access control and other restrictions, if a
client performs a base object search of the root with filter
"(objectClass=*)" requesting the desired attributes. It is noted that
root DSE attributes are operational, and like other operational
attributes, are not returned in search requests unless requested by
name.
The root DSE SHALL NOT be included if the client performs a subtree
search starting from the root.
Servers may allow clients to modify attributes of the root DSE where
appropriate.
The following attributes of the root DSE are defined in [Syntaxes].
Additional attributes may be defined in other documents.
- altServer: alternative servers;
- namingContexts: naming contexts;
- supportedControl: recognized LDAP controls;
- supportedExtension: recognized LDAP extended operations;
- supportedLDAPVersion: LDAP versions supported; and
- supportedSASLMechanisms: recognized SASL mechnanisms.
The values of these attributes provided may depend on a session
specific and other factors. For example, a server supporting the SASL
EXTERNAL mechanism may only list "EXTERNAL" when the client's identity
has been established by a lower level. See [AuthMeth].
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The root DSE may also include a 'subschemaSubentry' attribute. If so,
it refers to the subschema (sub)entry holding schema controlling
attributes of the root DSE. Client SHOULD NOT assume that the
subschema (sub)entry controlling the root DSE controls any entry held
by the server. General subschema discovery procedures are provided in
Section 4.4.
5.1.1. 'altServer'
The 'altServer' attribute lists URLs referring to alternative servers
which may be contacted when this server becomes unavailable. If the
server does not know of any other servers which could be used this
attribute will be absent. Clients may cache this information in case
their preferred LDAP server later becomes unavailable.
( 1.3.6.1.4.1.1466.101.120.6 NAME 'altServer'
SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 USAGE dSAOperation )
The IA5String (1.3.6.1.4.1.1466.115.121.1.26) syntax is defined in
[Syntaxes].
5.1.2. 'namingContexts'
The 'namingContexts' attribute lists the context prefixes of the
naming contexts the server masters or shadows (in part or in whole).
If the server does not master or shadow any information (e.g. it is an
LDAP gateway to a public X.500 directory) this attribute will be
absent. If the server believes it masters or shadows the entire
directory, the attribute will have a single value, and that value will
be the empty string (indicating the null DN of the root). This
attribute allows a client to choose suitable base objects for
searching when it has contacted a server.
( 1.3.6.1.4.1.1466.101.120.5 NAME 'namingContexts'
SYNTAX 1.3.6.1.4.1.1466.115.121.1.12 USAGE dSAOperation )
The DistinguishedName (1.3.6.1.4.1.1466.115.121.1.12) syntax is
defined in [Syntaxes].
5.1.3. 'supportedControl'
The 'supportedControl' attribute lists object identifiers identifying
the request controls the server supports. If the server does not
support any request controls, this attribute will be absent.
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Object identifiers identifying response controls need not be listed.
Procedures for registering object identifiers used to discovery of
protocol mechanisms are detailed in [LDAPIANA].
( 1.3.6.1.4.1.1466.101.120.13 NAME 'supportedControl'
SYNTAX 1.3.6.1.4.1.1466.115.121.1.38 USAGE dSAOperation )
The OBJECT IDENTIFIER (1.3.6.1.4.1.1466.115.121.1.38) syntax is
defined in [Syntaxes].
5.1.4. 'supportedExtension'
The 'supportedExtension' attribute lists object identifiers
identifying the extended operations which the server supports. If the
server does not support any extended operations, this attribute will
be absent.
An extended operation comprises a ExtendedRequest, possibly other PDUs
defined by extension, and an ExtendedResponse [Protocol]. The object
identifier assigned to the ExtendedRequest is used to identify the
extended operation. Other object identifiers associated with the
extended operation need not be listed.
Procedures for registering object identifiers used to discovery of
protocol mechanisms are detailed in [LDAPIANA].
( 1.3.6.1.4.1.1466.101.120.7 NAME 'supportedExtension'
SYNTAX 1.3.6.1.4.1.1466.115.121.1.38 USAGE dSAOperation )
The OBJECT IDENTIFIER (1.3.6.1.4.1.1466.115.121.1.38) syntax is
defined in [Syntaxes].
5.1.5. 'supportedLDAPVersion'
The 'supportedLDAPVersion' attribute lists the versions of LDAP which
the server supports.
( 1.3.6.1.4.1.1466.101.120.15 NAME 'supportedLDAPVersion'
SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 USAGE dSAOperation )
The INTEGER (1.3.6.1.4.1.1466.115.121.1.27) syntax are defined in
[Syntaxes].
5.1.6. 'supportedSASLMechanisms'
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The 'supportedSASLMechanisms' attribute lists the SASL mechanisms
[RFC2222] which the server recognizes. The contents of this attribute
may depend on the current session state. If the server does not
support any SASL mechanisms this attribute will not be present.
( 1.3.6.1.4.1.1466.101.120.14 NAME 'supportedSASLMechanisms'
SYNTAX 1.3.6.1.4.1.1466.115.121.1.15 USAGE dSAOperation )
The DirectoryString (1.3.6.1.4.1.1466.115.121.1.15) syntax is defined
in [Syntaxes].
6. Other Considerations
6.1. Preservation of User Information
Syntaxes may be defined which have specific value and/or value form
(representation) preservation requirements. For example, a syntax
containing digitally signed data can mandate the server preserve both
the value and form of value presented to ensure signature is not
invalidated.
Where such requirements have not be explicitly stated, servers SHOULD
preserve the value of user information but MAY return the value in a
different form. Where a server is unable (or unwilling) to preserve
the value of user information, the server SHALL ensure that an
equivalent value is returned. Two values are considered equivalent if
they would match according to the equality matching rule of the
associated attribute as evaluated (within variances allowed by the
rule's specification) on that server. If the attribute is defined
with no equality matching rule, two values are equivalent only if and
only if they are identical.
6.2. Short Names
Short names (descriptors) used to identify various schema elements are
non-unique, as two different specifications (neither in Standards
Track RFCs) may choose the same name. The client can retrieve the
subschema (as described above) to determine the element identified (in
that subschema) by a particular short name.
Procedures for registering short names are detailed in [LDAPIANA].
Specifications of schema elements should use registered short names to
avoid conflicts.
6.3. Cache and Shadowing
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Some servers may hold cache or shadow copies of entries, which can be
used to answer search and comparison queries, but will return
referrals or contact other servers if modification operations are
requested. Servers that perform shadowing or caching MUST ensure that
they do not violate any access control constraints placed on the data
by the originating server.
7. Implementation Guidelines
7.1 Server Guidelines
Servers MUST recognize all attribute types and object classes defined
in this document but, unless stated otherwise, need not support the
associated functionality. Servers SHOULD recognize all the names of
object classes defined in Section 7 of [Schema].
Servers MUST ensure that entries conform to user and system schema
rules or other data model constraints.
Servers MAY support DIT Content Rules, DIT Structural Rules, and/or
Name Forms features. To indicate support, servers SHOULD provide in
the subschema the definitions of attribute types associated with the
features they support.
Servers MAY support alias entries. To indicate support for alias
entries, servers SHOULD provide definitions for 'alias' and
'aliasedObjectName' in subschema (sub)entries.
Servers MAY support subentries. If so, they MUST do so in accordance
with [X.501]. Servers which do not support subenties SHOULD use
object entries to mimic subentries as detailed in Section 3.2.
Servers MAY support the 'extensibleObject' object class. To indicate
support for 'extensibleObject', servers SHOULD provide the
'extensibleObject' definition in subschema (sub)entries.
Servers MAY implement additional object classes. Servers SHOULD
provide the definitions of all object classes they support in
subschema (sub)entries.
7.2 Client Guidelines
Clients MUST NOT display nor attempt to decode as ASN.1, a value if
its syntax is not known. The implementation may attempt to discover
the subschema of the source entry, and retrieve the values of
'attributeTypes' from the subschema (sub)entry.
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Clients MUST NOT assume the LDAP-specific string encoding is
restricted to a UTF-8 encoded string of UCS characters or any
particular subset of particular subset of UCS (such as a printable
subset) unless such restriction is explicitly stated.
Clients MUST NOT send attribute values in a request that are not valid
according to the syntax defined for the attributes.
8. Security Considerations
Attributes of directory entries are used to provide descriptive
information about the real-world objects they represent, which can be
people, organizations or devices. Most countries have privacy laws
regarding the publication of information about people.
General security considerations for accessing directory information
with LDAP are discussed in [Protocol] and [AuthMeth].
9. IANA Considerations
It is requested that IANA update the LDAP descriptors registry as
indicated the following template:
Subject: Request for LDAP Descriptor Registration Update
Descriptor (short name): see comment
Object Identifier: see comment
Person & email address to contact for further information:
Kurt Zeilenga <kurt@OpenLDAP.org>
Usage: see comment
Specification: RFC XXXX
Author/Change Controller: IESG
Comments:
The following descriptors should be updated to refer to RFC XXXX.
NAME Type OID
------------------------ ---- -----------------
alias O 2.5.6.1
aliasedEntryName A 2.5.4.1
aliasedObjectName A 2.5.4.1
altServer A 1.3.6.1.4.1.1466.101.120.6
attributeTypes A 2.5.21.5
createTimestamp A 2.5.18.1
creatorsName A 2.5.18.3
dITContentRules A 2.5.21.2
dITStructureRules A 2.5.21.1
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extensibleObject O 1.3.6.1.4.1.1466.101.120.111
ldapSyntaxes A 1.3.6.1.4.1.1466.101.120.16
matchingRuleUse A 2.5.21.8
matchingRules A 2.5.21.4
modifiersName A 2.5.18.4
modifyTimestamp A 2.5.18.2
nameForms A 2.5.21.7
namingContexts A 1.3.6.1.4.1.1466.101.120.5
objectClass A 2.5.4.0
objectClasses A 2.5.21.6
subschema O 2.5.20.1
subschemaSubentry A 2.5.18.10
supportedControl A 1.3.6.1.4.1.1466.101.120.13
supportedExtension A 1.3.6.1.4.1.1466.101.120.7
supportedLDAPVersion A 1.3.6.1.4.1.1466.101.120.15
supportedSASLMechanisms A 1.3.6.1.4.1.1466.101.120.14
top O 2.5.6.0
10. Acknowledgments
This document is based, in part, on [RFC2251] by M. Wahl, T. Howes,
and S. Kille and [RFC2252] by M. Wahl, A. Coulbeck, T. Howes, S.
Kille, both products of the IETF Access, Searching and Indexing of
Directories (ASID) Working Group. This document is also based, in
part, on "The Directory: Models" [X.501], a product of the
International Telephone Union (ITU).
11. Author's Address
Kurt Zeilenga
E-mail: <kurt@openldap.org>
12. References
12.1. Normative References
[RFC2279] Yergeau, F., "UTF-8, a transformation format of ISO 10646",
RFC 2279, January 1998.
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14 (also RFC 2119), March 1997.
[RFC2234] Crocker, D., and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
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[Roadmap] K. Zeilenga (editor), "LDAP: Technical Specification Road
Map", draft-ietf-ldapbis-roadmap-xx.txt, a work in
progress.
[Protocol] J. Sermersheim (editor), "LDAP: The Protocol",
draft-ietf-ldapbis-protocol-xx.txt, a work in progress.
[AuthMeth] R. Harrison (editor), "LDAP: Authentication Methods and
Connection Level Security Mechanisms",
draft-ietf-ldapbis-authmeth-xx.txt, a work in progress.
[LDAPDN] K. Zeilenga (editor), "LDAP: String Representation of
Distinguished Names", draft-ietf-ldapbis-dn-xx.txt, a work
in progress.
[Filters] M. Smith (editor), LDAPbis WG, "LDAP: String Representation
of Search Filters", draft-ietf-ldapbis-filter-xx.txt, a
work in progress.
[LDAPURL] M. Smith (editor), "LDAP: Uniform Resource Locator",
draft-ietf-ldapbis-url-xx.txt, a work in progress.
[Syntaxes] K. Dally (editor), "LDAP: Syntaxes",
draft-ietf-ldapbis-syntaxes-xx.txt, a work in progress.
[Schema] K. Dally (editor), "LDAP: User Schema",
draft-ietf-ldapbis-user-schema-xx.txt, a work in progress.
[LDAPIANA] K. Zeilenga, "IANA Considerations for LDAP",
draft-ietf-ldapbis-xx.txt (a work in progress).
[ISO10646] Universal Multiple-Octet Coded Character Set (UCS) -
Architecture and Basic Multilingual Plane, ISO/IEC 10646-1
: 1993.
[X.500] ITU-T Rec. X.500, "The Directory: Overview of Concepts,
Models and Service", 1993.
[X.501] ITU-T Rec. X.501, "The Directory: Models", 1993.
[X.511] ITU-T Rec. X.511, "The Directory: Abstract Service
Definition", 1993.
[X.680] ITU-T Rec. X.680, "Abstract Syntax Notation One (ASN.1) -
Specification of Basic Notation", 1994.
12.2. Informative References
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[RFC2251] M. Wahl, T. Howes, S. Kille, "Lightweight Directory Access
Protocol (v3)", RFC 2251, December 1997.
[RFC2252] M. Wahl, A. Coulbeck, T. Howes, S. Kille, "Lightweight
Directory Access Protocol (v3): Attribute Syntax
Definitions", RFC 2252, December 1997.
[LDAPTS] J. Hodges, R.L. Morgan, "Lightweight Directory Access
Protocol (v3): Technical Specification",
draft-ietf-ldapbis-ldapv3-ts-xx.txt.
Appendix A. Changes
This appendix is non-normative.
This document amounts to nearly a complete rewrite of portions of RFC
2251, RFC 2252, and RFC 2256. This rewrite was undertaken to improve
overall clarity of technical specification. This appendix provides a
summary of substantive changes made to the portions of these documents
incorporated into this document. Readers should consult [Roadmap],
[Protocol], [Syntaxes], and [Schema] for summaries of remaining
portions of these documents.
A.1 Changes to RFC 2251
This document incorporates from RFC 2251 sections 3.2 and 3.4,
portions of Section 4 and 6 as summarized below.
A.1.1 Section 3.2 of RFC 2251
Section 3.2 of RFC 2251 provided a brief introduction to the X.500
data model, as used by LDAP. The previous specification relied on
[X.501] but lacked clarity in how X.500 models are adapted for use by
LDAP. This document describes the X.500 data models, as used by LDAP
in greater detail, especially in areas where the models require
adaptation is needed.
Section 3.2.1 of RFC 2251 described an attribute as "a type with one
or more associated values." In LDAP, an attribute is better described
as an attribute description, a type with zero or options, and one or
more associated values.
Section 3.2.2 of RFC 2251 mandated that subschema subentries contain
objectClasses and attributeTypes attributes, yet X.500(93) treats
these attributes as optional. While generally all implementations
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support X.500(93) subschema mechanisms will provide both of these
attributes, it is not absolutely required for interoperability that
all servers do. The mandate was removed for consistency with
X.500(93). The subschema discovery mechanism was also clarified to
indicate that subschema controlling an entry is obtained by reading
the (sub)entry referred to by that entry's 'subschemaSubentry'
attribute.
A.1.2 Section 3.4 of RFC 2251
Section 3.4 of RFC 2251 provided "Server-specific Data Requirements".
This material, with changes, was incorporated in Section 5.1 of this
document.
Changes:
- Clarify that attributes of the root DSE are subject to "other
restrictions" in addition to acccess controls.
- Clarify that only recognized extended requests need to be enumerated
'supportedExtension'.
- Clarify that only recognized request controls need to be enumerated
'supportedControl'.
- Clarify that root DSE attributes are operational and, like other
operational attributes, will not be returned in search requests
unless requested by name.
- Clarify that not all root DSE attributes are user modifiable.
- Remove inconsistent text regarding handling of the
'subschemaSubentry' attribute within the root DSE. The previous
specification stated that the 'subschemaSubentry' attribute held in
the root DSE referred to "subschema entries (or subentries) known by
this server." This is inconsistent with the attribute intended use
as well as its formal definition as a single valued attribute
[X.501]. It is also noted that a simple (possibly incomplete) list
of subschema (sub)entries is not terrible useful. This document (in
section 5.1) specifies that the 'subschemaSubentry' attribute of the
root DSE refers to the subschema controlling the root DSE. It is
noted that the general subschema discovery mechanism remains
available (see Section 4.4 of this document).
A.1.2 Section 4 of RFC 2251
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Portions of Section 4 of RFC 2251 detailing aspects of the information
model used by LDAP were incorporated in this document, including:
- Restriction of distinguished values to attributes whose descriptions
have no options (from Section 4.1.3).
- Data model aspects of Attribute Types (from Section 4.1.4),
Attribute Descriptions (from 4.1.4), Attribute (from 4.1.8),
Matching Rule Identifer (from 4.1.9).
- User schema requirements (from Section 4.1.6, 4.5.1, and 4.7).
A.1.3 Section 6 of RFC 2251
The Section 6.1 and the second paragraph of Section 6.2 of RFC 2251
where incorporated into this document.
A.2 Changes to RFC 2252
This document incorporates Sections 4, 5 and 7 from RFC 2252.
A.2.1 Section 4 of RFC 2252
The specification was updated to use Augmented BNF [RFC2234]. The
string representation of an OBJECT IDENTIFIER was tighten to
disallow leading zeros as described in RFC 2252 text.
The <descr> syntax was changed to disallow semicolon (U+0003B)
characters to appear to be consistent its natural language
specification "descr is the syntactic representation of an object
descriptor, which consists of letters and digits, starting with a
letter." In a related change, the statement "an
AttributeDescription can be used as the value in a NAME part of an
AttributeTypeDescription" was deleted. RFC 2252 provided no
specification as to the semantics of attribute options appearing in
NAME fields.
The ABNF for a quoted string (qdstring) was updated to reflect
support for the eescaping mechanism described in 4.3 of RFC 2252.
A.2.2 Section 5 of RFC 2252
Definitions of operational attributes provided in Section 5 of RFC
2252 where incorporated into this document.
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The 'supportedExtension' description was clarified. A server need
only list the OBJECT IDENTIFIERs associated with the extended
requests of the extended operations it recognizes.
The 'supportedControl' description was clarified. A server need
only list the OBJECT IDENTIFIERs associated with the request
controls it recognizes.
A.2.3 Section 7 of RFC 2252
Section 7 of RFC 2252 provides definitions of the 'subschema' and
'extensibleObject' object classes. These definitions where
integrated into Section 4.2 and Section 4.3 of this document,
respectively. Section 7 of RFC 2252 also contained the object class
implementation requirement. This was incorporated into Section 7 of
this document.
The specification of 'extensibleObject' was clarified of how it
interacts with precluded attributes.
A.3 Changes to RFC 2256
This document incorporates Sections 5.1, 5.2, 7.1, and 7.2 of RFC
2256.
Section 5.1 of RFC 2256 provided the definition of the 'objectClass'
attribute type. This was integrated into Section 2.4.1 of this
document. The statement "One of the values is either 'top' or
'alias'" was replaced with statement that one of the values is 'top'
as entries belonging to 'alias' also belong to 'top'.
Section 5.2 of RFC 2256 provided the definition of the
'aliasedObjectName' attribute type. This was integrated into
Section 2.6.2 of this document.
Section 7.1 of RFC 2256 provided the definition of the 'top' object
class. This was integrated into Section 2.4.1 of this document.
Section 7.2 of RFC 2256 provided the definition of the 'alias'
object class. This was integrated into Section 2.6.1 of this
document.
Copyright 2002, The Internet Society. All Rights Reserved.
This document and translations of it may be copied and furnished to
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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 AUTHORS, 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.
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