Network Working Group K. Zeilenga Request for Comments: 4512 OpenLDAP Foundation Obsoletes: 2251, 2252, 2256, 3674 June 2006 Category: Standards Track Lightweight Directory Access Protocol (LDAP): Directory Information Models Status of This Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2006). Abstract The Lightweight Directory Access Protocol (LDAP) is an Internet protocol for accessing distributed directory services that act in accordance with X.500 data and service models. This document describes the X.500 Directory Information Models, as used in LDAP. Zeilenga Standards Track [Page 1]
RFC 4512 LDAP Models June 2006 Table of Contents 1. Introduction ....................................................3 1.1. Relationship to Other LDAP Specifications ..................3 1.2. Relationship to X.501 ......................................4 1.3. Conventions ................................................4 1.4. Common ABNF Productions ....................................4 2. Model of Directory User Information .............................6 2.1. The Directory Information Tree .............................7 2.2. Structure of an Entry ......................................7 2.3. Naming of Entries ..........................................8 2.4. Object Classes .............................................9 2.5. Attribute Descriptions ....................................12 2.6. Alias Entries .............................................16 3. Directory Administrative and Operational Information ...........17 3.1. Subtrees ..................................................17 3.2. Subentries ................................................18 3.3. The 'objectClass' attribute ...............................18 3.4. Operational Attributes ....................................19 4. Directory Schema ...............................................22 4.1. Schema Definitions ........................................23 4.2. Subschema Subentries ......................................32 4.3. 'extensibleObject' object class ...........................35 4.4. Subschema Discovery .......................................35 5. DSA (Server) Informational Model ...............................36 5.1. Server-Specific Data Requirements .........................36 6. Other Considerations ...........................................40 6.1. Preservation of User Information ..........................40 6.2. Short Names ...............................................41 6.3. Cache and Shadowing .......................................41 7. Implementation Guidelines ......................................42 7.1. Server Guidelines .........................................42 7.2. Client Guidelines .........................................42 8. Security Considerations ........................................43 9. IANA Considerations ............................................43 10. Acknowledgements ..............................................44 11. Normative References ..........................................45 Appendix A. Changes ...............................................47 A.1. Changes to RFC 2251 .......................................47 A.2. Changes to RFC 2252 .......................................49 A.3. Changes to RFC 2256 .......................................50 A.4. Changes to RFC 3674 .......................................51 Zeilenga Standards Track [Page 2]
RFC 4512 LDAP Models June 2006 1. Introduction This document discusses the X.500 Directory Information Models [X.501], as used by the Lightweight Directory Access Protocol (LDAP) [RFC4510]. 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 distribution knowledge and replication knowledge information models) may be adapted for use in LDAP. Specification of how these models apply to LDAP is left to future documents. 1.1. Relationship to Other LDAP Specifications This document is a integral part of the LDAP technical specification [RFC4510], which obsoletes the previously defined LDAP technical specification, RFC 3377, in its entirety. This document obsoletes RFC 2251, Sections 3.2 and 3.4, as well as portions of Sections 4 and 6. Appendix A.1 summarizes changes to these sections. The remainder of RFC 2251 is obsoleted by the [RFC4511], [RFC4513], and [RFC4510] documents. Zeilenga Standards Track [Page 3]
RFC 4512 LDAP Models June 2006 This document obsoletes RFC 2252, Sections 4, 5, and 7. Appendix A.2 summarizes changes to these sections. The remainder of RFC 2252 is obsoleted by [RFC4517]. 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 [RFC4519] and [RFC4517]. This document obsoletes RFC 3674 in its entirety. Appendix A.4 summarizes changes since RFC 3674. 1.2. Relationship to X.501 This document includes material, with and without adaptation, from [X.501] as necessary to describe this protocol. These adaptations (and any other differences herein) apply to this protocol, and only this protocol. 1.3. 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 definitions are specified in [RFC4517]. 1.4. Common ABNF Productions A number of syntaxes in this document are described using Augmented Backus-Naur Form (ABNF) [RFC4234]. 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 " " Zeilenga Standards Track [Page 4]
RFC 4512 LDAP Models June 2006 NULL = %x00 ; null (0) SPACE = %x20 ; space (" ") DQUOTE = %x22 ; quote (""") SHARP = %x23 ; octothorpe (or sharp sign) ("#") DOLLAR = %x24 ; dollar sign ("$") SQUOTE = %x27 ; single quote ("'") LPAREN = %x28 ; left paren ("(") RPAREN = %x29 ; right paren (")") PLUS = %x2B ; plus sign ("+") COMMA = %x2C ; comma (",") HYPHEN = %x2D ; hyphen ("-") DOT = %x2E ; period (".") SEMI = %x3B ; semicolon (";") LANGLE = %x3C ; left angle bracket ("<") EQUALS = %x3D ; equals sign ("=") RANGLE = %x3E ; right angle bracket (">") ESC = %x5C ; backslash ("\") USCORE = %x5F ; underscore ("_") LCURLY = %x7B ; left curly brace "{" RCURLY = %x7D ; right curly brace "}" ; Any UTF-8 [RFC3629] encoded Unicode [Unicode] character UTF8 = UTF1 / UTFMB UTFMB = UTF2 / UTF3 / UTF4 UTF0 = %x80-BF UTF1 = %x00-7F UTF2 = %xC2-DF UTF0 UTF3 = %xE0 %xA0-BF UTF0 / %xE1-EC 2(UTF0) / %xED %x80-9F UTF0 / %xEE-EF 2(UTF0) UTF4 = %xF0 %x90-BF 2(UTF0) / %xF1-F3 3(UTF0) / %xF4 %x80-8F 2(UTF0) OCTET = %x00-FF ; Any octet (8-bit data unit) Object identifiers (OIDs) [X.680] are represented in LDAP using a dot-decimal format conforming to the ABNF: numericoid = number 1*( DOT number ) Short names, also known as descriptors, are used as more readable aliases for object identifiers. Short names are case insensitive and conform to the ABNF: descr = keystring Zeilenga Standards Track [Page 5]
RFC 4512 LDAP Models June 2006 Where either an object identifier or a short name may be specified, the following production is used: oid = descr / numericoid While the <descr> form is generally preferred when the usage is restricted to short names referring to object identifiers that identify like kinds of objects (e.g., attribute type descriptions, matching rule descriptions, object class descriptions), the <numericoid> form should be used when the object identifiers may identify multiple kinds of objects or when an unambiguous short name (descriptor) is not available. Implementations SHOULD treat short names (descriptors) used in an ambiguous manner (as discussed above) as unrecognized. Short Names (descriptors) are discussed further in Section 6.2. 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. There are multiple kinds of directory entries. 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 the structure of entries. Section 2.3 discusses naming of entries. Zeilenga Standards Track [Page 6]
RFC 4512 LDAP Models June 2006 Section 2.4 discusses object classes. Section 2.5 discusses attribute descriptions. 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 are the entry's immediate superior and its superiors. An entry's subordinates are all of its immediate subordinates and their subordinates. Similarly, the superior/subordinate relationship between object entries can be used to derive a relation between the objects they represent. DIT structure rules can be used to govern relationships between objects. Note: An entry's immediate superior is also known as the entry's parent, and an entry's immediate subordinate is also known as the entry's child. Entries that have the same parent are known as siblings. 2.2. Structure of an Entry An entry consists of a set of attributes that hold information about the object that the entry represents. Some attributes represent user information and are called user attributes. Other attributes represent operational and/or administrative information and are called operational attributes. An attribute is an attribute description (a type and zero or more options) with one or more associated values. An attribute is often referred to by its attribute description. For example, the 'givenName' attribute is the attribute that consists of the attribute description 'givenName' (the 'givenName' attribute type [RFC4519] and zero options) and 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. Attribute values conform to the defined syntax of the attribute type. Zeilenga Standards Track [Page 7]
RFC 4512 LDAP Models June 2006 No two values of an attribute may be equivalent. Two values are considered equivalent if and only if they would match according to the equality matching rule of the attribute type. Or, if the attribute type is defined with no equality matching rule, two values are equivalent if and only if they are identical. (See 2.5.1 for other restrictions.) For example, a 'givenName' attribute can have more than one value, they must be Directory Strings, and they are case insensitive. A 'givenName' attribute cannot hold both "John" and "JOHN", as these are equivalent values per the equality matching rule of the attribute type. Additionally, no attribute is to have a value that is not equivalent to itself. For example, the 'givenName' attribute cannot have as a value a directory string that includes the REPLACEMENT CHARACTER (U+FFFD) code point, as matching involving that directory string is Undefined per this attribute's equality matching rule. When an attribute is used for naming of the entry, one and only one value of the attribute is used in forming the Relative Distinguished Name. This value is known as a distinguished value. 2.3. Naming of Entries 2.3.1. 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 an unordered set of one or more attribute value assertions (AVA) consisting of an attribute description with zero options and an attribute value. These AVAs are chosen to match attribute values (each a distinguished value) of the entry. An entry's relative distinguished name must be unique among all immediate subordinates of the entry's immediate superior (i.e., all siblings). The following are examples of string representations of RDNs [RFC4514]: UID=12345 OU=Engineering CN=Kurt Zeilenga+L=Redwood Shores The last is an example of a multi-valued RDN; that is, an RDN composed of multiple AVAs. Zeilenga Standards Track [Page 8]
RFC 4512 LDAP Models June 2006 2.3.2. 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 examples of string representations of DNs [RFC4514]: UID=nobody@example.com,DC=example,DC=com CN=John Smith,OU=Sales,O=ACME Limited,L=Moab,ST=Utah,C=US 2.3.3. 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. 2.4. Object Classes An object class is "an identified family of objects (or conceivable objects) that share certain characteristics" [X.501]. As defined in [X.501]: Object classes are used in the Directory for a number of purposes: - describing and categorizing 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. Zeilenga Standards Track [Page 9]
RFC 4512 LDAP Models June 2006 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 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 its superclass 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, or Auxiliary. Each object class is identified by an object identifier (OID) and, optionally, one or more short names (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 an abstract object class unless it belongs to a structural or auxiliary class that inherits from that abstract class. Abstract object classes cannot derive from structural or 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'. The following is the object class definition (see Section 4.1.1) for the 'top' object class: ( 2.5.6.0 NAME 'top' ABSTRACT MUST objectClass ) All entries belong to the 'top' abstract object class. Zeilenga Standards Track [Page 10]
RFC 4512 LDAP Models June 2006 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 characterized 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. 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. 2.4.3. Auxiliary Object Classes Auxiliary object classes are used to augment the characteristics of entries. They are commonly used to augment the sets of attributes required and allowed 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. Zeilenga Standards Track [Page 11]
RFC 4512 LDAP Models June 2006 An entry can belong to any subset of the set of auxiliary object classes allowed by the DIT content rule associated with the structural object class of the entry. If no DIT content rule is associated with the structural object class of the entry, the entry cannot belong to any auxiliary object class. The set of auxiliary object classes that 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: 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 that 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 with an unrecognized attribute type is to be treated as unrecognized. Servers SHALL treat an attribute description with an unrecognized attribute option as unrecognized. Clients MAY treat an unrecognized 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. Zeilenga Standards Track [Page 12]
RFC 4512 LDAP Models June 2006 If no equality matching is specified for the attribute type: - the attribute (of the type) cannot be used for naming; - when adding the attribute (or replacing all values), no two values may be equivalent (see 2.2); - individual values of a multi-valued attribute are not to be independently added or deleted; - attribute value assertions (such as matching in search filters and comparisons) using values of such a type cannot be performed. Otherwise, the specified equality matching rule is to be used to evaluate attribute value assertions concerning the attribute type. The specified equality rule is to be transitive and commutative. The attribute type indicates whether the attribute is a user attribute or an operational attribute. If operational, the attribute type indicates the operational usage and whether or not the attribute is modifiable by users. Operational attributes are discussed in Section 3.4. An attribute type (a subtype) may derive from a more generic attribute type (a direct supertype). The following restrictions apply to subtyping: - a subtype must have the same usage as its direct supertype, - a subtype's syntax must be the same, or a refinement of, its supertype's syntax, and - a subtype must be collective [RFC3671] if its supertype is collective. An attribute description consisting of a subtype and no options is said to be 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 (descriptors). 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. Zeilenga Standards Track [Page 13]
RFC 4512 LDAP Models June 2006 Not all options can be used 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 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 BCP 64, RFC 4520 [RFC4520]. 2.5.2.1. Tagging Options Attributes held in the directory can have attribute descriptions with any number of tagging options. Tagging options are never mutually exclusive. An attribute description with N tagging options is 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 a direct (description) subtype of the attribute description of the supertype and the N tagging options. That is, 'cn;lang-de;lang-en' is a direct (description) subtype of 'cn;lang-de', 'cn;lang-en', and 'name;lang-de;lang-en' ('cn' is a subtype of 'name'; both are defined in [RFC4519]). 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. Zeilenga Standards Track [Page 14]
RFC 4512 LDAP Models June 2006 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 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 user modification of entry content. An attribute value stored in an object or alias entry is of precisely one attribute description. The description is indicated when the value is originally added to the entry. For the purpose of subschema administration of the entry, a specification that an attribute is required is fulfilled if the entry contains a value of an attribute description belonging to an attribute hierarchy where the attribute type of that description is the same as the required attribute's type. That is, a "MUST name" specification is fulfilled by 'name' or 'name;x-tag-option', but is not fulfilled by 'CN' or 'CN;x-tag-option' (even though 'CN' is a subtype of 'name'). Likewise, an entry may contain a value of an attribute description belonging to an attribute hierarchy where the attribute type of that description is either explicitly included in the definition of an object class to which the entry belongs or allowed by the DIT content rule applicable to that entry. That is, 'name' and 'name;x-tag-option' are allowed by "MAY name" (or by "MUST name"), but 'CN' and 'CN;x-tag-option' are not allowed by "MAY name" (or by "MUST name"). Zeilenga Standards Track [Page 15]
RFC 4512 LDAP Models June 2006 For the purposes of other policy administration, unless stated otherwise in the specification of the particular administrative model, all of the attribute descriptions in an attribute hierarchy are treated as distinct and unrelated descriptions. 2.6. Alias Entries As adapted from [X.501]: An alias, or an alias name, for an object is 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. 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. An entry with the 'alias' object class must also belong to an object class (or classes), or be governed by a DIT content rule, which allows suitable naming attributes to be present. Example: dn: cn=bar,dc=example,dc=com objectClass: top objectClass: alias objectClass: extensibleObject Zeilenga Standards Track [Page 16]
RFC 4512 LDAP Models June 2006 cn: bar aliasedObjectName: cn=foo,dc=example,dc=com 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 are defined in [RFC4517]. 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 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. Zeilenga Standards Track [Page 17]
RFC 4512 LDAP Models June 2006 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 detailed in [RFC3672]. The term "(sub)entry" in this specification indicates that servers implementing X.500(93) models are, in accordance with X.500(93) as described in [RFC3672], to use a subentry and that other servers are to 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 [RFC4519] (as all subentries are named with 'cn'). 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 the OBJECT IDENTIFIER (1.3.6.1.4.1.1466.115.121.1.38) syntax are defined in [RFC4517]. The 'objectClass' attribute specifies the object classes of an entry, which (among other things) are used in conjunction with the controlling 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 that follow X.500(93) models SHALL restrict modifications of this attribute to prevent the basic structural class of the entry from being changed. That is, one cannot change a 'person' into a 'country'. When creating an entry or adding an 'objectClass' value to an entry, all superclasses of the named classes SHALL be implicitly added as well if not already present. That is, if the auxiliary class 'x-a' is a subclass of the class 'x-b', adding 'x-a' to 'objectClass' causes 'x-b' to be implicitly added (if is not already present). Servers SHALL restrict modifications of this attribute to prevent superclasses of remaining 'objectClass' values from being deleted. That is, if the auxiliary class 'x-a' is a subclass of the auxiliary Zeilenga Standards Track [Page 18]
RFC 4512 LDAP Models June 2006 class 'x-b' and the 'objectClass' attribute contains 'x-a' and 'x-b', an attempt to delete only 'x-b' from the 'objectClass' attribute is an error. 3.4. Operational Attributes Some attributes, termed operational attributes, are used or maintained by servers for administrative and operational purposes. As stated in [X.501]: "There are three varieties of operational attributes: Directory operational attributes, DSA-shared operational attributes, and DSA-specific operational attributes". A directory operational attribute is used to represent operational and/or administrative information in the Directory Information Model. This includes operational attributes maintained by the server (e.g., 'createTimestamp') as well as operational attributes that hold values administrated by the user (e.g., 'ditContentRules'). A DSA-shared operational attribute is used to represent information of the DSA Information Model that is shared between DSAs. A DSA-specific operational attribute is used to represent information of the DSA Information Model that is specific to the DSA (though, in some cases, may be derived from information shared between DSAs; e.g., 'namingContexts'). The DSA Information Model operational attributes are detailed in [X.501]. Operational attributes are not normally visible. They are not returned in search results unless explicitly requested by name. Not all operational attributes are user modifiable. 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, and - modifyTimestamp: the time this entry was last modified. Zeilenga Standards Track [Page 19]
RFC 4512 LDAP Models June 2006 Servers SHOULD maintain the 'creatorsName', 'createTimestamp', 'modifiersName', and 'modifyTimestamp' attributes for all entries of the DIT. 3.4.1. 'creatorsName' This attribute appears in entries that were added using the protocol (e.g., using the Add operation). The value is the distinguished 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 [RFC4517]. 3.4.2. 'createTimestamp' This attribute appears in entries that 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 [RFC4517]. 3.4.3. 'modifiersName' This attribute appears in entries that have been modified using the protocol (e.g., using the Modify operation). The value is the distinguished 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 ) Zeilenga Standards Track [Page 20]
RFC 4512 LDAP Models June 2006 The 'distinguishedNameMatch' matching rule and the DistinguishedName (1.3.6.1.4.1.1466.115.121.1.12) syntax are defined in [RFC4517]. 3.4.4. 'modifyTimestamp' This attribute appears in entries that 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 rules and the GeneralizedTime (1.3.6.1.4.1.1466.115.121.1.24) syntax are defined in [RFC4517]. 3.4.5. 'structuralObjectClass' This attribute indicates the structural object class of the entry. ( 2.5.21.9 NAME 'structuralObjectClass' EQUALITY objectIdentifierMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.38 SINGLE-VALUE NO-USER-MODIFICATION USAGE directoryOperation ) The 'objectIdentifierMatch' matching rule and OBJECT IDENTIFIER (1.3.6.1.4.1.1466.115.121.1.38) syntax is defined in [RFC4517]. 3.4.6. 'governingStructureRule' This attribute indicates the structure rule governing the entry. ( 2.5.21.10 NAME 'governingStructureRule' EQUALITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE NO-USER-MODIFICATION USAGE directoryOperation ) The 'integerMatch' matching rule and INTEGER (1.3.6.1.4.1.1466.115.121.1.27) syntax is defined in [RFC4517]. Zeilenga Standards Track [Page 21]
RFC 4512 LDAP Models June 2006 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 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; Zeilenga Standards Track [Page 22]
RFC 4512 LDAP Models June 2006 e) Attribute Type definitions that identify the object identifier 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 Syntax 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 WSP oidlist WSP RPAREN ) oidlist = oid *( WSP DOLLAR WSP oid ) extensions = *( SP xstring SP qdstrings ) xstring = "X" HYPHEN 1*( ALPHA / HYPHEN / USCORE ) qdescrs = qdescr / ( LPAREN WSP qdescrlist WSP RPAREN ) qdescrlist = [ qdescr *( SP qdescr ) ] qdescr = SQUOTE descr SQUOTE qdstrings = qdstring / ( LPAREN WSP qdstringlist WSP RPAREN ) qdstringlist = [ qdstring *( SP qdstring ) ] qdstring = SQUOTE dstring SQUOTE dstring = 1*( QS / QQ / QUTF8 ) ; escaped UTF-8 string QQ = ESC %x32 %x37 ; "\27" QS = ESC %x35 ( %x43 / %x63 ) ; "\5C" / "\5c" ; Any UTF-8 encoded Unicode character ; except %x27 ("\'") and %x5C ("\") QUTF8 = QUTF1 / UTFMB ; 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. Zeilenga Standards Track [Page 23]
RFC 4512 LDAP Models June 2006 The NAME field provides a set of short names (descriptors) that are to 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. The OBSOLETE field, if present, indicates the element is not active. 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 are followed by <SP> and <qdstrings> tokens. 4.1.1. Object Class Definitions Object Class definitions are written according to the ABNF: ObjectClassDescription = LPAREN WSP numericoid ; object identifier [ SP "NAME" SP qdescrs ] ; short names (descriptors) [ 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 (descriptors) identifying this object class; DESC <qdstring> is a short 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 (the default is STRUCTURAL); MUST and MAY specify the sets of required and allowed attribute types, respectively; and <extensions> describe extensions. Zeilenga Standards Track [Page 24]
RFC 4512 LDAP Models June 2006 4.1.2. Attribute Types Attribute Type definitions are written according to the ABNF: AttributeTypeDescription = LPAREN WSP numericoid ; object identifier [ SP "NAME" SP qdescrs ] ; short names (descriptors) [ SP "DESC" SP qdstring ] ; description [ SP "OBSOLETE" ] ; not active [ SP "SUP" SP oid ] ; supertype [ 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" / ; user "directoryOperation" / ; directory operational "distributedOperation" / ; DSA-shared operational "dSAOperation" ; DSA-specific operational where: <numericoid> is object identifier assigned to this attribute type; NAME <qdescrs> are short names (descriptors) identifying this attribute type; DESC <qdstring> is a short descriptive string; OBSOLETE indicates this attribute type is not active; SUP oid specifies the direct supertype of this type; EQUALITY, ORDERING, and SUBSTR provide the oid of the equality, ordering, and substrings matching rules, respectively; SYNTAX identifies value syntax by object identifier and may suggest a minimum upper bound; SINGLE-VALUE indicates attributes of this type are restricted to a single value; COLLECTIVE indicates this attribute type is collective [X.501][RFC3671]; 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. If no SYNTAX field is provided, the attribute type description takes its value from the supertype. Zeilenga Standards Track [Page 25]
RFC 4512 LDAP Models June 2006 If SUP field is provided, the EQUALITY, ORDERING, and SUBSTRING fields, if not specified, take their value from the supertype. Usage of userApplications, the default, indicates that attributes of this type represent user information. That is, they are user attributes. A usage of directoryOperation, distributedOperation, or dSAOperation indicates that attributes of this type represent operational and/or administrative information. That is, they are operational attributes. directoryOperation usage indicates that the attribute of this type is a directory operational attribute. distributedOperation usage indicates that the attribute of this type is a DSA-shared usage operational attribute. dSAOperation usage indicates that the attribute of this type is a DSA-specific operational attribute. COLLECTIVE requires usage userApplications. Use of collective attribute types in LDAP is discussed in [RFC3671]. NO-USER-MODIFICATION requires an operational usage. Note that the <AttributeTypeDescription> does not list the matching rules that can be used with that attribute type in an extensibleMatch search filter [RFC4511]. This is done using the 'matchingRuleUse' attribute described in Section 4.1.4. 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 minimum 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 [RFC3629] is a variable-length encoding. Zeilenga Standards Track [Page 26]
RFC 4512 LDAP Models June 2006 4.1.3. Matching Rules Matching rules are used in performance of attribute value assertions, such as in performance of a Compare operation. They are also used in evaluating search filters, determining which individual values are to be added or deleted during performance of a Modify operation, and in comparing distinguished names. Each matching rule is identified by an object identifier (OID) and, optionally, one or more short names (descriptors). Matching rule definitions are written according to the ABNF: MatchingRuleDescription = LPAREN WSP numericoid ; object identifier [ SP "NAME" SP qdescrs ] ; short names (descriptors) [ SP "DESC" SP qdstring ] ; description [ SP "OBSOLETE" ] ; not active SP "SYNTAX" SP numericoid ; assertion syntax extensions WSP RPAREN ; extensions where: <numericoid> is object identifier assigned to this matching rule; NAME <qdescrs> are short names (descriptors) identifying this matching rule; DESC <qdstring> is a short descriptive string; OBSOLETE indicates this matching rule is not active; SYNTAX identifies the assertion syntax (the syntax of the assertion value) by object identifier; and <extensions> describe extensions. 4.1.4. Matching Rule Uses A matching rule use lists the attribute types that are suitable for use with an extensibleMatch search filter. Matching rule use descriptions are written according to the following ABNF: MatchingRuleUseDescription = LPAREN WSP numericoid ; object identifier [ SP "NAME" SP qdescrs ] ; short names (descriptors) [ SP "DESC" SP qdstring ] ; description [ SP "OBSOLETE" ] ; not active SP "APPLIES" SP oids ; attribute types extensions WSP RPAREN ; extensions Zeilenga Standards Track [Page 27]
RFC 4512 LDAP Models June 2006 where: <numericoid> is the object identifier of the matching rule associated with this matching rule use description; NAME <qdescrs> are short names (descriptors) identifying this matching rule use; DESC <qdstring> is a short 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. 4.1.5. 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 a string of Unicode [Unicode] characters in UTF-8 [RFC3629] form. Each LDAP syntax is identified by an object identifier (OID). LDAP syntax definitions are written according to the ABNF: SyntaxDescription = LPAREN WSP numericoid ; object identifier [ SP "DESC" SP qdstring ] ; description extensions WSP RPAREN ; extensions where: <numericoid> is the object identifier assigned to this LDAP syntax; DESC <qdstring> is a short descriptive string; and <extensions> describe extensions. 4.1.6. DIT Content Rules A DIT content rule is a "rule governing the content of entries of a particular structural object class" [X.501]. For DIT entries of a particular structural object class, a DIT content rule specifies 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 the rule, the structural object class, or any of the allowed auxiliary object classes. Zeilenga Standards Track [Page 28]
RFC 4512 LDAP Models June 2006 Each content rule is identified by the object identifier, as well as any short names (descriptors), of the structural object class 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 attributes 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 that 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 rules for superclasses of the structural object class of an entry are not applicable to that entry. DIT content rule descriptions are written according to the ABNF: DITContentRuleDescription = LPAREN WSP numericoid ; object identifier [ SP "NAME" SP qdescrs ] ; short names (descriptors) [ 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 (descriptors) identifying this DIT content rule; DESC <qdstring> is a short descriptive string; OBSOLETE indicates this DIT content rule use is not active; AUX specifies a list of auxiliary object classes that entries subject to this DIT content rule may belong to; Zeilenga Standards Track [Page 29]
RFC 4512 LDAP Models June 2006 MUST, MAY, and NOT specify lists of attribute types that are required, allowed, or precluded, respectively, from appearing in entries subject to this DIT content rule; and <extensions> describe extensions. 4.1.7. DIT Structure Rules and Name Forms It is sometimes desirable to regulate where object and alias entries can be placed in the DIT and how they can be named based upon their structural object class. 4.1.7.1. DIT Structure Rules A DIT structure 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]. DIT structure rule descriptions are written according to the ABNF: DITStructureRuleDescription = LPAREN WSP ruleid ; rule identifier [ SP "NAME" SP qdescrs ] ; short names (descriptors) [ 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 (descriptors) identifying this DIT structure rule; DESC <qdstring> is a short descriptive string; OBSOLETE indicates this DIT structure rule use is not active; FORM is specifies the name form associated with this DIT structure rule; SUP identifies superior rules (by rule id); and <extensions> describe extensions. Zeilenga Standards Track [Page 30]
RFC 4512 LDAP Models June 2006 If no superior rules are identified, the DIT structure rule applies to an autonomous administrative point (e.g., the root vertex of the subtree controlled by the subschema) [X.501]. 4.1.7.2. Name Forms 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 attribute types. A particular attribute type cannot be in both sets. 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 (descriptors). Name form descriptions are written according to the ABNF: NameFormDescription = LPAREN WSP numericoid ; object identifier [ SP "NAME" SP qdescrs ] ; short names (descriptors) [ 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 that identifies this name form; NAME <qdescrs> are short names (descriptors) identifying this name form; DESC <qdstring> is a short 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. All attribute types in the required ("MUST") and allowed ("MAY") lists shall be different. Zeilenga Standards Track [Page 31]
RFC 4512 LDAP Models June 2006 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 that follow X.500(93) models SHOULD implement subschema using the X.500 subschema mechanisms (as detailed in Section 12 of [X.501]), 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 subschema modification. Procedures for subschema modification are discussed in Section 14.5 of [X.501]. A server that masters entries and permits clients to modify these entries SHALL implement and provide access to these subschema (sub)entries including providing a 'subschemaSubentry' attribute in each modifiable entry. This is so clients may discover the attributes and object classes that are permitted to be present. It is strongly RECOMMENDED that all other servers implement this as well. 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 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 [RFC4517]. 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. Zeilenga Standards Track [Page 32]
RFC 4512 LDAP Models June 2006 Servers MAY provide additional attributes (described in other documents) in subschema (sub)entries. 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. ( 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 [RFC4517]. 4.2.2. 'attributeTypes' This attribute holds definitions of attribute types. ( 2.5.21.5 NAME 'attributeTypes' EQUALITY objectIdentifierFirstComponentMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.3 USAGE directoryOperation ) The 'objectIdentifierFirstComponentMatch' matching rule and the AttributeTypeDescription (1.3.6.1.4.1.1466.115.121.1.3) syntax are defined in [RFC4517]. 4.2.3. 'matchingRules' This attribute holds definitions of matching rules. ( 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 [RFC4517]. Zeilenga Standards Track [Page 33]
RFC 4512 LDAP Models June 2006 4.2.4 'matchingRuleUse' This attribute holds definitions of matching rule uses. ( 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 [RFC4517]. 4.2.5. 'ldapSyntaxes' This attribute holds definitions of LDAP syntaxes. ( 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 [RFC4517]. 4.2.6. 'dITContentRules' This attribute lists DIT Content Rules that are present in the subschema. ( 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 [RFC4517]. Zeilenga Standards Track [Page 34]
RFC 4512 LDAP Models June 2006 4.2.7. 'dITStructureRules' This attribute lists DIT Structure Rules that are present in the subschema. ( 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 [RFC4517]. 4.2.8 'nameForms' This attribute lists Name Forms that 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 [RFC4517]. 4.3. 'extensibleObject' object class The 'extensibleObject' auxiliary object class allows entries that belong to it to hold any user attribute. The set of allowed attribute types of this object class is implicitly the set of all attribute types of userApplications usage. ( 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. 4.4. Subschema Discovery To discover the DN of the subschema (sub)entry holding the subschema controlling a particular entry, a client reads that entry's 'subschemaSubentry' operational attribute. To read schema attributes from the subschema (sub)entry, clients MUST issue a Search operation [RFC4511] where baseObject is the DN of the subschema (sub)entry, Zeilenga Standards Track [Page 35]
RFC 4512 LDAP Models June 2006 scope is baseObject, filter is "(objectClass=subschema)" [RFC4515], and the attributes field lists the names of the desired schema attributes (as they are operational). Note: the "(objectClass=subschema)" filter allows LDAP servers that gateway to X.500 to detect that subentry information is being requested. Clients SHOULD NOT assume that a published subschema is complete, that the server supports all of the schema elements it publishes, or that the server does not support an unpublished element. 5. DSA (Server) Informational Model The LDAP protocol assumes there are one or more servers that jointly provide access to a Directory Information Tree (DIT). The server holding the original information is called the "master" (for that information). Servers that hold copies of the original information are referred to as "shadowing" or "caching" servers. 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. 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 including all its subordinates and their subordinates, down to the entries that are mastered by different servers. 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 SHALL 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, which is named with the DN with zero RDNs (whose [RFC4514] representation is as the zero-length string). These attributes are retrievable, subject to access control and other restrictions, if a client performs a Search operation [RFC4511] with an empty baseObject, scope of baseObject, the filter Zeilenga Standards Track [Page 36]
RFC 4512 LDAP Models June 2006 "(objectClass=*)" [RFC4515], and the attributes field listing the names of 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 below. Additional attributes may be defined in other documents. - altServer: alternative servers; - namingContexts: naming contexts; - supportedControl: recognized LDAP controls; - supportedExtension: recognized LDAP extended operations; - supportedFeatures: recognized LDAP features; - supportedLDAPVersion: LDAP versions supported; and - supportedSASLMechanisms: recognized Simple Authentication and Security Layers (SASL) [RFC4422] mechanisms. The values provided for these attributes may depend on session- specific and other factors. For example, a server supporting the SASL EXTERNAL mechanism might only list "EXTERNAL" when the client's identity has been established by a lower level. See [RFC4513]. The root DSE may also include a 'subschemaSubentry' attribute. If it does, the attribute refers to the subschema (sub)entry holding the schema controlling the root DSE. Clients SHOULD NOT assume that this subschema (sub)entry controls other entries held by the server. General subschema discovery procedures are provided in Section 4.4. Zeilenga Standards Track [Page 37]
RFC 4512 LDAP Models June 2006 5.1.1. 'altServer' The 'altServer' attribute lists URIs referring to alternative servers that may be contacted when this server becomes unavailable. URIs for servers implementing the LDAP are written according to [RFC4516]. Other kinds of URIs may be provided. If the server does not know of any other servers that could be used, this attribute will be absent. Clients may cache this information in case their preferred 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 [RFC4517]. 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 is a first-level DSA [X.501], it should list (in addition) an empty string (indicating the root of the DIT). 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 root of the DIT). This attribute may be used, for example, to select a suitable entry name for subsequent operations with this 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 [RFC4517]. 5.1.3. 'supportedControl' The 'supportedControl' attribute lists object identifiers identifying the request controls [RFC4511] the server supports. If the server does not support any request controls, this attribute will be absent. Object identifiers identifying response controls need not be listed. Procedures for registering object identifiers used to discovery of protocol mechanisms are detailed in BCP 64, RFC 4520 [RFC4520]. Zeilenga Standards Track [Page 38]
RFC 4512 LDAP Models June 2006 ( 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 [RFC4517]. 5.1.4. 'supportedExtension' The 'supportedExtension' attribute lists object identifiers identifying the extended operations [RFC4511] that the server supports. If the server does not support any extended operations, this attribute will be absent. An extended operation generally consists of an extended request and an extended response but may also include other protocol data units (such as intermediate responses). The object identifier assigned to the extended request is used to identify the extended operation. Other object identifiers used in the extended operation need not be listed as values of this attribute. Procedures for registering object identifiers used to discovery of protocol mechanisms are detailed in BCP 64, RFC 4520 [RFC4520]. ( 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 [RFC4517]. 5.1.5. 'supportedFeatures' The 'supportedFeatures' attribute lists object identifiers identifying elective features that the server supports. If the server does not support any discoverable elective features, this attribute will be absent. ( 1.3.6.1.4.1.4203.1.3.5 NAME 'supportedFeatures' EQUALITY objectIdentifierMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.38 USAGE dSAOperation ) Procedures for registering object identifiers used to discovery of protocol mechanisms are detailed in BCP 64, RFC 4520 [RFC4520]. The OBJECT IDENTIFIER (1.3.6.1.4.1.1466.115.121.1.38) syntax and objectIdentifierMatch matching rule are defined in [RFC4517]. Zeilenga Standards Track [Page 39]
RFC 4512 LDAP Models June 2006 5.1.6. 'supportedLDAPVersion' The 'supportedLDAPVersion' attribute lists the versions of LDAP that 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 is defined in [RFC4517]. 5.1.7. 'supportedSASLMechanisms' The 'supportedSASLMechanisms' attribute lists the SASL mechanisms [RFC4422] that the server recognizes and/or supports [RFC4513]. 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 Directory String (1.3.6.1.4.1.1466.115.121.1.15) syntax is defined in [RFC4517]. 6. Other Considerations 6.1. Preservation of User Information Syntaxes may be defined that have specific value and/or value form (representation) preservation requirements. For example, a syntax containing digitally signed data can mandate that the server preserve both the value and form of value presented to ensure that the signature is not invalidated. Where such requirements have not been explicitly stated, servers SHOULD preserve the value of user information but MAY return the value in a different form. And where a server is unable (or unwilling) to preserve the value of user information, the server SHALL ensure that an equivalent value (per Section 2.3) is returned. Zeilenga Standards Track [Page 40]
RFC 4512 LDAP Models June 2006 6.2. Short Names Short names, also known as descriptors, are used as more readable aliases for object identifiers and are used to identify various schema elements. However, it is not expected that LDAP implementations with human user interface would display these short names (or the object identifiers they refer to) to the user. Instead, they would most likely be performing translations (such as expressing the short name in one of the local national languages). For example, the short name "st" (stateOrProvinceName) might be displayed to a German-speaking user as "Land". The same short name might have different meaning in different subschemas, and, within a particular subschema, the same short name might refer to different object identifiers each identifying a different kind of schema element. Implementations MUST be prepared that the same short name might be used in a subschema to refer to the different kinds of schema elements. That is, there might be an object class 'x-fubar' and an attribute type 'x-fubar' in a subschema. Implementations MUST be prepared that the same short name might be used in the different subschemas to refer to the different schema elements. That is, there might be two matching rules 'x-fubar', each in different subschemas. Procedures for registering short names (descriptors) are detailed in BCP 64, RFC 4520 [RFC4520]. 6.3. Cache and Shadowing 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. Zeilenga Standards Track [Page 41]
RFC 4512 LDAP Models June 2006 7. Implementation Guidelines 7.1. Server Guidelines Servers MUST recognize all names of 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 attribute types and object classes defined in Section 3 and 4, respectively, of [RFC4519]. Servers MUST ensure that entries conform to user and system schema rules or other data model constraints. Servers MAY support DIT Content Rules. Servers MAY support DIT Structure Rules and Name Forms. Servers MAY support alias entries. Servers MAY support the 'extensibleObject' object class. Servers MAY support subentries. If so, they MUST do so in accordance with [RFC3672]. Servers that do not support subentries SHOULD use object entries to mimic subentries as detailed in Section 3.2. Servers MAY implement additional schema elements. Servers SHOULD provide definitions of all schema elements they support in subschema (sub)entries. 7.2. Client Guidelines In the absence of prior agreements with servers, clients SHOULD NOT assume that servers support any particular schema elements beyond those referenced in Section 7.1. The client can retrieve subschema information as described in Section 4.4. Clients MUST NOT display or attempt to decode a value as ASN.1 if the value's syntax is not known. Clients MUST NOT assume the LDAP- specific string encoding is restricted to a UTF-8 encoded string of Unicode characters or any particular subset of Unicode (such as a printable subset) unless such restriction is explicitly stated. Clients SHOULD NOT send attribute values in a request that are not valid according to the syntax defined for the attributes. Zeilenga Standards Track [Page 42]
RFC 4512 LDAP Models June 2006 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 [RFC4511] and [RFC4513]. 9. IANA Considerations The Internet Assigned Numbers Authority (IANA) has updated the LDAP descriptors registry as indicated in 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 4512 Author/Change Controller: IESG Comments: The following descriptors (short names) has been added to the registry. NAME Type OID ------------------------ ---- ----------------- governingStructureRule A 2.5.21.10 structuralObjectClass A 2.5.21.9 The following descriptors (short names) have been updated to refer to this RFC. NAME Type OID ------------------------ ---- ----------------- alias O 2.5.6.1 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 extensibleObject O 1.3.6.1.4.1.1466.101.120.111 ldapSyntaxes A 1.3.6.1.4.1.1466.101.120.16 Zeilenga Standards Track [Page 43]
RFC 4512 LDAP Models June 2006 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 supportedFeatures A 1.3.6.1.4.1.4203.1.3.5 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. Acknowledgements This document is based in part on RFC 2251 by M. Wahl, T. Howes, and S. Kille; RFC 2252 by M. Wahl, A. Coulbeck, T. Howes, S. Kille; and RFC 2556 by M. Wahl, all 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). Additional text was borrowed from RFC 2253 by M. Wahl, T. Howes, and S. Kille. This document is a product of the IETF LDAP Revision (LDAPBIS) Working Group. Zeilenga Standards Track [Page 44]
RFC 4512 LDAP Models June 2006 11. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. [RFC3671] Zeilenga, K., "Collective Attributes in the Lightweight Directory Access Protocol (LDAP)", RFC 3671, December 2003. [RFC3672] Zeilenga, K., "Subentries in the Lightweight Directory Access Protocol (LDAP)", RFC 3672, December 2003. [RFC4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 4234, October 2005. [RFC4422] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple Authentication and Security Layer (SASL)", RFC 4422, June 2006. [RFC4510] Zeilenga, K., Ed., "Lightweight Directory Access Protocol (LDAP): Technical Specification Road Map", RFC 4510, June 2006. [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access Protocol (LDAP): The Protocol", RFC 4511, June 2006. [RFC4513] Harrison, R., Ed., "Lightweight Directory Access Protocol (LDAP): Authentication Methods and Security Mechanisms", RFC 4513, June 2006. [RFC4514] Zeilenga, K., Ed., "Lightweight Directory Access Protocol (LDAP): String Representation of Distinguished Names", RFC 4514, June 2006. [RFC4515] Smith, M., Ed. and T. Howes, "Lightweight Directory Access Protocol (LDAP): String Representation of Search Filters", RFC 4515, June 2006. [RFC4516] Smith, M., Ed. and T. Howes, "Lightweight Directory Access Protocol (LDAP): Uniform Resource Locator", RFC 4516, June 2006. [RFC4517] Legg, S., Ed., "Lightweight Directory Access Protocol (LDAP): Syntaxes and Matching Rules", RFC 4517, June 2006. Zeilenga Standards Track [Page 45]
RFC 4512 LDAP Models June 2006 [RFC4519] Sciberras, A., Ed., "Lightweight Directory Access Protocol (LDAP): Schema for User Applications", RFC 4519, June 2006. [RFC4520] Zeilenga, K., "Internet Assigned Numbers Authority (IANA) Considerations for the Lightweight Directory Access Protocol (LDAP)", BCP 64, RFC 4520, June 2006. [Unicode] The Unicode Consortium, "The Unicode Standard, Version 3.2.0" is defined by "The Unicode Standard, Version 3.0" (Reading, MA, Addison-Wesley, 2000. ISBN 0-201- 61633-5), as amended by the "Unicode Standard Annex #27: Unicode 3.1" (http://www.unicode.org/reports/tr27/) and by the "Unicode Standard Annex #28: Unicode 3.2" (http://www.unicode.org/reports/tr28/). [X.500] International Telecommunication Union - Telecommunication Standardization Sector, "The Directory -- Overview of concepts, models and services," X.500(1993) (also ISO/IEC 9594-1:1994). [X.501] International Telecommunication Union - Telecommunication Standardization Sector, "The Directory -- Models," X.501(1993) (also ISO/IEC 9594- 2:1994). [X.680] International Telecommunication Union - Telecommunication Standardization Sector, "Abstract Syntax Notation One (ASN.1) - Specification of Basic Notation", X.680(2002) (also ISO/IEC 8824-1:2002). Zeilenga Standards Track [Page 46]
RFC 4512 LDAP Models June 2006 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 [RFC4510], [RFC4511], [RFC4517], and [RFC4519] 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, and portions of Sections 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 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 more 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 that 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. Zeilenga Standards Track [Page 47]
RFC 4512 LDAP Models June 2006 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 access 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's 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 terribly 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.1.3. Section 4 of RFC 2251 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); Zeilenga Standards Track [Page 48]
RFC 4512 LDAP Models June 2006 - Data model aspects of Attribute Types (from Section 4.1.4), Attribute Descriptions (from 4.1.5), Attribute (from 4.1.8), Matching Rule Identifier (from 4.1.9); and - User schema requirements (from Sections 4.1.6, 4.5.1, and 4.7). Clarifications to these portions include: - Subtyping and AttributeDescriptions with options. A.1.4. 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 [RFC4234]. The string representation of an OBJECT IDENTIFIER was tightened to disallow leading zeros as described in RFC 2252. The <descr> syntax was changed to disallow semicolon (U+003B) characters in order 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 of the semantics of attribute options appearing in NAME fields. RFC 2252 stated that the <descr> form of <oid> SHOULD be preferred over the <numericoid> form. However, <descr> form can be ambiguous. To address this issue, the imperative was replaced with a statement (in Section 1.4) that while the <descr> form is generally preferred, <numericoid> should be used where an unambiguous <descr> is not available. Additionally, an expanded discussion of descriptor issues is in Section 6.2 ("Short Names"). The ABNF for a quoted string (qdstring) was updated to reflect support for the escaping mechanism described in Section 4.3 of RFC 2252. Zeilenga Standards Track [Page 49]
RFC 4512 LDAP Models June 2006 A.2.2. Section 5 of RFC 2252 Definitions of operational attributes provided in Section 5 of RFC 2252 where incorporated into this document. The 'namingContexts' description was clarified. A first-level DSA should publish, in addition to other values, "" indicating the root of the DIT. The 'altServer' description was clarified. It may hold any URI. 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. Descriptions for the 'structuralObjectClass' and 'governingStructureRule' operational attribute types were added. The attribute definition of 'subschemaSubentry' was corrected to list the terms SINGLE-VALUE and NO-USER-MODIFICATION in proper order. 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 regarding 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'. Zeilenga Standards Track [Page 50]
RFC 4512 LDAP Models June 2006 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. A.4. Changes to RFC 3674 This document made no substantive change to the 'supportedFeatures' technical specification provided in RFC 3674. Editor's Address Kurt D. Zeilenga OpenLDAP Foundation EMail: Kurt@OpenLDAP.org Zeilenga Standards Track [Page 51]
RFC 4512 LDAP Models June 2006 Full Copyright Statement Copyright (C) The Internet Society (2006). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgement Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Zeilenga Standards Track [Page 52]
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