Internet Draft

Network Working Group                                            M. Wahl
INTERNET-DRAFT                                       Critical Angle Inc.
Obsoletes: RFC 1778                                          A. Coulbeck
                                                              Isode Inc.
                                                                T. Howes
                                           Netscape Communications Corp.
                                                                S. Kille
                                                           Isode Limited
Intended Category: Standards Track                          11 July 1997


                  Lightweight Directory Access Protocol (v3):
                       Attribute Syntax Definitions
                 <draft-ietf-asid-ldapv3-attributes-06.txt> 

1. Status of this Memo

   This document is an Internet-Draft.  Internet-Drafts are working 
   documents of the Internet Engineering Task Force (IETF), its areas, and
   its working groups.  Note that other groups may also distribute working
   documents as Internet-Drafts.
 
   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference material
   or to cite them other than as "work in progress."
 
   To learn the current status of any Internet-Draft, please check the
   "1id-abstracts.txt" listing  contained in the Internet-Drafts Shadow
   Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe),
   ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim).

2. Abstract

   The Lightweight Directory Access Protocol (LDAP) [1] requires that 
   the contents of AttributeValue fields in protocol elements be octet 
   strings.  This document defines a set of syntaxes for LDAPv3, and the
   rules by which attribute values of these syntaxes are represented as
   octet strings for transmission in the LDAP protocol.  The syntaxes 
   defined in this document are referenced by this and other documents 
   that define attribute types.  This document also defines the set of 
   attribute types which LDAP servers should support.

3. Overview

   This document defines the framework for developing schemas for 
   directories accessible via the Lightweight Directory Access Protocol.

   Schema is the collection of attribute type definitions, object class
   definitions and other information which a server uses to determine
   how to match a filter or attribute value assertion (in a compare 
   operation) against the attributes of an entry, and whether to permit 
   add and modify operations.  

   Section 4 states the general requirements and notations for attribute
   types, object classes, syntax and matching rule definitions.

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   Section 5 lists attributes, section 6 syntaxes and section 7 object 
   classes.

   Additional documents define schemas for representing real-world 
   objects as directory entries.

4. General Issues

   This document describes encodings used in an Internet protocol. 

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in 
   this document are to be interpreted as described in RFC 2119 [4].

   Attribute Type and Object Class definitions are written in a 
   string representation of the AttributeTypeDescription and 
   ObjectClassDescription data types defined in X.501(93) [3].  
   Implementors are strongly advised to first read the description
   of how schema is represented in X.500 before reading the rest of 
   this document.

4.1. Common Encoding Aspects

   For the purposes of defining the encoding rules for attribute 
   syntaxes, the following BNF definitions will be used.  They are 
   based on the BNF styles of RFC 822 [13].

     a     = "a" / "b" / "c" / "d" / "e" / "f" / "g" / "h" / "i" /
             "j" / "k" / "l" / "m" / "n" / "o" / "p" / "q" / "r" /
             "s" / "t" / "u" / "v" / "w" / "x" / "y" / "z" / "A" /
             "B" / "C" / "D" / "E" / "F" / "G" / "H" / "I" / "J" /
             "K" / "L" / "M" / "N" / "O" / "P" / "Q" / "R" / "S" /
             "T" / "U" / "V" / "W" / "X" / "Y" / "Z"

     d               = "0" / "1" / "2" / "3" / "4" / 
                       "5" / "6" / "7" / "8" / "9"

     hex-digit       =  d / "a" / "b" / "c" / "d" / "e" / "f" /
                            "A" / "B" / "C" / "D" / "E" / "F"

     k               = a / d / "-"

     p               = a / d / """ / "(" / ")" / "+" / "," / 
                       "-" / "." / "/" / ":" / "?" / " "

     letterstring    = 1*a

     numericstring   = 1*d

     anhstring       = 1*k

     keystring       = a [ anhstring ]

     printablestring = 1*p

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     space           = 1*" " 

     whsp            = [ space ]

     utf8            = 

     dstring         = 1*utf8

     qdstring        = whsp "'" dstring "'" whsp

     qdstringlist    = ( qdstringlist qdstring ) / ""

     qdstrings       = qdstring / ( whsp "(" qdstringlist ")" whsp )

   In the following BNF for the string representation of OBJECT 
   IDENTIFIERs, descr is the syntactic representation of an object 
   descriptor, which consists of letters and digits, starting with a 
   letter.  An OBJECT IDENTIFIER in the numericoid format should not 
   have leading zeroes (e.g. "0.9.3" is permitted but "0.09.3" should 
   not be generated).

   When encoding values in syntax, the descr encoding option SHOULD
   be used in preference to the numericoid. An object descriptor is
   a more readable alias for a number OBJECT IDENTIFIER, and these 
   (where assigned and known by the implementation) SHOULD be used in
   preference to numeric oids to the greatest extent possible.  
   Examples of object descriptors in LDAP are attribute type, object 
   class and matching rule names. 
 
     oid             = descr / numericoid 

     descr           = keystring 

     numericoid      = numericstring *( "." numericstring )

     woid            = whsp oid whsp

     ; set of oids of either form
     oids            = woid / ( "(" oidlist ")" )

     oidlist         = woid *( "$" woid )

     ; object descriptors used as schema element names
     qdescrs         = qdescr / ( whsp "(" qdescrlist ")" whsp )

     qdescrlist      = ( qdescrlist qdescr ) / ""

     qdescr          = whsp "'" descr "'" whsp







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4.2. Attribute Types

   The attribute types are described by sample values for the subschema 
   "attributeTypes" attribute, which is written in the 
   AttributeTypeDescription syntax.  While lines have been folded for 
   readability, the values transferred in protocol would not contain 
   newlines.  

   The AttributeTypeDescription is encoded according to the following 
   BNF, and the productions for oid, qdsescrs and qdstring are given
   in section 4.1.  Implementors should note that future versions of this
   document may have expanded this BNF to include additional terms.

      AttributeTypeDescription = "(" whsp
            numericoid whsp              ; AttributeType identifier
          [ "NAME" qdescrs ]             ; name used in AttributeType
          [ "DESC" qdstring ]            ; description
          [ "OBSOLETE" whsp ]
          [ "SUP" woid ]                 ; derived from this other 
                                         ; AttributeType
          [ "EQUALITY" woid              ; Matching Rule name
          [ "ORDERING" woid              ; Matching Rule name
          [ "SUBSTR" woid ]              ; Matching Rule name 
          [ "SYNTAX" whsp noidlen whsp ] ; see section 4.3
          [ "SINGLE-VALUE" whsp ]        ; default multi-valued
          [ "COLLECTIVE" whsp ]          ; default not collective
          [ "NO-USER-MODIFICATION" whsp ]; default user modifiable
          [ "USAGE" whsp AttributeUsage ]; default user applications
          whsp ")"
    
      AttributeUsage =
          "userApplications"     /
          "directoryOperation"   /
          "distributedOperation" / ; DSA-shared
          "dSAOperation"          ; DSA-specific, value depends on server

   Servers are not required to provide the same or any text 
   in the description part of the subschema values they maintain.
   Servers SHOULD provide at least one of the "SUP" and "SYNTAX" fields 
   for each AttributeTypeDescription.

   Servers SHOULD implement all the attribute types referenced in 
   section 5.  Servers MUST be able to evaluate presence filters, 
   SHOULD be able to perform equality matching of values of all user 
   attributes known to the server, and MAY be able to perform matching
   with the other kinds of filters.  If a server allows values of an 
   attribute of a particular type to be added or removed over protocol, 
   the server MUST be able to perform equality matching of values of 
   that attribute, but need not perform any additional validity checks 
   on attribute values.
   
   Servers MAY recognize additional names and attributes not listed in 
   this document, and if they do so, MUST publish the definitions of 
   the types in the attributeTypes attribute of their subschema 
   entries.  

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   Schema developers MUST NOT create attribute definitions whose names
   conflict with attributes defined for use with LDAP in existing 
   standards-track RFCs.

   AttributeDescriptions can be used as the value in a NAME part of an
   AttributeTypeDescription.  Note that these are case insensitive.

   Note that the AttributeTypeDescription does not list the matching 
   rules which can can be used with that attribute type in an 
   extensibleMatch search filter.  This is done using the matchingRuleUse
   attribute described in section 4.5.

   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, and an optional indication of the maximum length of
   a value of this attribute.

4.3. Syntaxes

   This section defines general requirements for LDAP attribute value
   syntax encodings. All documents defining attribute syntax encodings 
   for use with LDAP are expected to conform to these requirements.

   The encoding rules defined for a given attribute syntax must produce
   octet strings.  To the greatest extent possible, encoded octet
   strings should be usable in their native encoded form for display
   purposes. In particular, encoding rules for attribute syntaxes
   defining non-binary values should produce strings that can be
   displayed with little or no translation by clients implementing 
   LDAP.  There are a few cases (e.g. audio) however, when it is not 
   sensible to produce a printable representation, and clients MUST NOT 
   assume that an unrecognized syntax is a string representation.

   In encodings where an arbitrary string is used as part of a larger 
   production (other than a Distinguished Name), a backslash quoting 
   mechanism is used to encode the following separator symbol character 
   (such as "'", "$" or "#") if it should occur in that string.  The 
   backslash is followed by a pair of hexadecimal digits representing the
   next character.  A backslash itself in the string which forms part of 
   a larger syntax is always transmitted as '\5C' or '\5c'.

   Syntaxes are also defined for matching rules whose assertion value 
   syntax is different from the attribute value syntax.

4.3.1  Binary Transfer of Values

   This encoding format is used if the binary encoding is requested by 
   the client for an attribute, or if the attribute syntax name is 
   "1.3.6.1.4.1.1466.115.121.1.5".  The value, an instance of the ASN.1 
   AttributeValue type, is BER-encoded, subject to the restrictions of 
   section 5.1 of [1], and this sequence of octets is used as the value. 
   (E.g. the first byte inside the OCTET STRING wrapper is a tag byte. 
   However the OCTET STRING is still encoded in primitive form.)


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   All servers MUST implement this form for both generating attribute 
   values in search responses, and parsing attribute values in add, 
   compare and modify requests, if the attribute type is recognized and 
   the attribute syntax name is that of Binary.  Clients which request 
   that all attributes be returned from entries MUST be prepared 
   to receive values in binary (e.g. userCertificate), and SHOULD NOT 
   simply display binary or unrecognized values to users.

4.3.2. Syntax Object Identifiers

   Syntaxes for use with LDAP are named by OBJECT IDENTIFIERs, which
   are dotted-decimal strings.  These are not intended to be displayed 
   to users.

   noidlen = numericoid [ "{" len "}" ]

   len     = numericstring

   The following table lists some of the syntaxes that have been defined 
   for LDAP thus far.  The H-R column suggests whether a value in that 
   syntax would likely be a human readable string.  Clients and servers 
   need not implement all the syntaxes listed here, and MAY implement 
   other syntaxes.

   Other documents may define additional syntaxes.  However, the 
   definition of additional arbitrary syntaxes is strongly depreciated
   since it will hinder interoperability: today's client and server
   implementations generally do not have the ability to dynamically
   recognize new syntaxes.  In most cases attributes will be defined 
   with the syntax for directory strings.

   Value being represented        H-R OBJECT IDENTIFIER
   =================================================================
   ACI Item                        N  1.3.6.1.4.1.1466.115.121.1.1
   Access Point                    Y  1.3.6.1.4.1.1466.115.121.1.2
   Attribute Type Description      Y  1.3.6.1.4.1.1466.115.121.1.3
   Audio                           N  1.3.6.1.4.1.1466.115.121.1.4
   Binary                          N  1.3.6.1.4.1.1466.115.121.1.5
   Bit String                      Y  1.3.6.1.4.1.1466.115.121.1.6
   Boolean                         Y  1.3.6.1.4.1.1466.115.121.1.7
   Certificate                     N  1.3.6.1.4.1.1466.115.121.1.8
   Certificate List                N  1.3.6.1.4.1.1466.115.121.1.9
   Certificate Pair                N  1.3.6.1.4.1.1466.115.121.1.10
   Country String                  Y  1.3.6.1.4.1.1466.115.121.1.11
   DN                              Y  1.3.6.1.4.1.1466.115.121.1.12
   Data Quality Syntax             Y  1.3.6.1.4.1.1466.115.121.1.13
   Delivery Method                 Y  1.3.6.1.4.1.1466.115.121.1.14
   Directory String                Y  1.3.6.1.4.1.1466.115.121.1.15
   DIT Content Rule Description    Y  1.3.6.1.4.1.1466.115.121.1.16
   DIT Structure Rule Description  Y  1.3.6.1.4.1.1466.115.121.1.17
   DL Submit Permission            Y  1.3.6.1.4.1.1466.115.121.1.18
   DSA Quality Syntax              Y  1.3.6.1.4.1.1466.115.121.1.19
   DSE Type                        Y  1.3.6.1.4.1.1466.115.121.1.20
   Enhanced Guide                  Y  1.3.6.1.4.1.1466.115.121.1.21


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   Facsimile Telephone Number      Y  1.3.6.1.4.1.1466.115.121.1.22
   Fax                             N  1.3.6.1.4.1.1466.115.121.1.23
   Generalized Time                Y  1.3.6.1.4.1.1466.115.121.1.24
   Guide                           Y  1.3.6.1.4.1.1466.115.121.1.25
   IA5 String                      Y  1.3.6.1.4.1.1466.115.121.1.26
   INTEGER                         Y  1.3.6.1.4.1.1466.115.121.1.27
   JPEG                            N  1.3.6.1.4.1.1466.115.121.1.28
   LDAP Syntax Description         Y  1.3.6.1.4.1.1466.115.121.1.54
   Master And Shadow Access Points Y  1.3.6.1.4.1.1466.115.121.1.29
   Matching Rule Description       Y  1.3.6.1.4.1.1466.115.121.1.30
   Matching Rule Use Description   Y  1.3.6.1.4.1.1466.115.121.1.31
   Mail Preference                 Y  1.3.6.1.4.1.1466.115.121.1.32
   MHS OR Address                  Y  1.3.6.1.4.1.1466.115.121.1.33
   Modify Rights                   Y  1.3.6.1.4.1.1466.115.121.1.55
   Name And Optional UID           Y  1.3.6.1.4.1.1466.115.121.1.34
   Name Form Description           Y  1.3.6.1.4.1.1466.115.121.1.35
   Numeric String                  Y  1.3.6.1.4.1.1466.115.121.1.36
   Object Class Description        Y  1.3.6.1.4.1.1466.115.121.1.37
   OID                             Y  1.3.6.1.4.1.1466.115.121.1.38
   Other Mailbox                   Y  1.3.6.1.4.1.1466.115.121.1.39
   Password                        Y  1.3.6.1.4.1.1466.115.121.1.40
   Postal Address                  Y  1.3.6.1.4.1.1466.115.121.1.41
   Protocol Information            Y  1.3.6.1.4.1.1466.115.121.1.42
   Presentation Address            Y  1.3.6.1.4.1.1466.115.121.1.43
   Printable String                Y  1.3.6.1.4.1.1466.115.121.1.44
   Subtree Specification           Y  1.3.6.1.4.1.1466.115.121.1.45
   Supplier Information            Y  1.3.6.1.4.1.1466.115.121.1.46
   Supplier Or Consumer            Y  1.3.6.1.4.1.1466.115.121.1.47
   Supplier And Consumer           Y  1.3.6.1.4.1.1466.115.121.1.48
   Supported Algorithm             N  1.3.6.1.4.1.1466.115.121.1.49
   Telephone Number                Y  1.3.6.1.4.1.1466.115.121.1.50
   Teletex Terminal Identifier     Y  1.3.6.1.4.1.1466.115.121.1.51
   Telex Number                    Y  1.3.6.1.4.1.1466.115.121.1.52
   UTC Time                        Y  1.3.6.1.4.1.1466.115.121.1.53

   A suggested minimum upper bound on the number of characters in 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 name'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 byte 
   since UTF-8 is a variable-length encoding.

4.3.3. Syntax Description

   The following BNF may be used to associate a short description with
   a syntax OBJECT IDENTIFIER. Implementors should note that future 
   versions of this document may expand this definition to include 
   additional terms.




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      SyntaxDescription = "(" whsp
          numericoid whsp
          [ "DESC" qdstring ]
          whsp ")"

4.4. Object Classes

   The format for representation of object classes is defined in X.501 
   [3]. In general every entry will contain an abstract class ("top" or 
   "alias"), at least one structural object class, and zero or more 
   auxiliary object classes.  Whether an object class is abstract,
   structural or auxiliary is defined when the object class identifier 
   is assigned.  An object class definition should not be changed 
   without having a new identifier assigned to it.
   
   Object class descriptions are written according to the following BNF.
   Implementors should note that future versions of this document may 
   expand this definition to include additional terms.

      ObjectClassDescription = "(" whsp
          numericoid whsp      ; ObjectClass identifier
          [ "NAME" qdescrs ]
          [ "DESC" qdstring ]
          [ "OBSOLETE" whsp ]
          [ "SUP" oids ]       ; Superior ObjectClasses
          [ ( "ABSTRACT" / "STRUCTURAL" / "AUXILIARY" ) whsp ] 
                               ; default structural
          [ "MUST" oids ]      ; AttributeTypes
          [ "MAY" oids ]       ; AttributeTypes
      whsp ")"

   These are described as sample values for the subschema 
   "objectClasses" attribute for a server which implements the LDAP 
   schema. While lines have been folded for readability, the values 
   transferred in protocol would not contain newlines.

   Servers SHOULD implement all the object classes referenced in 
   section 7, except for extensibleObject, which is optional.

   Servers MAY implement additional object classes not listed in this 
   document, and if they do so, MUST publish the definitions of the 
   classes in the objectClasses attribute of their subschema entries.
   Later documents may define additional object classes.

   Schema developers MUST NOT create object class definitions whose 
   names conflict with attributes defined for use with LDAP in existing 
   standards-track RFCs.

4.5. Matching Rules

   Matching rules are used by servers to compare attribute values 
   against assertion values when performing Search and Compare 
   operations.  They are also used to identify the value to be added 
   or deleted when modifying entries, and are used when comparing a 
   purported distinguished name with the name of an entry.

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   Most of the attributes given in this document will have an equality 
   matching rule defined.

   Matching rule descriptions are written according to the following 
   BNF.  Implementors should note that future versions of this document 
   may have expanded this BNF to include additional terms.

      MatchingRuleDescription = "(" whsp
          numericoid whsp  ; MatchingRule identifier
          [ "NAME" qdescrs ]
          [ "DESC" qdstring ]
          [ "OBSOLETE" whsp ]
          "SYNTAX" numericoid 
      whsp ")"

   Values of the matchingRuleUse list the attributes which are suitable
   for use with an extensible matching rule.

      MatchingRuleUseDescription = "(" whsp
          numericoid whsp  ; MatchingRule identifier
          [ "NAME" qdescrs ]
          [ "DESC" qdstring ]
          [ "OBSOLETE" ]
         "APPLIES" oids    ; AttributeType identifiers
      whsp ")"

   Servers which support matching rules and the extensibleMatch SHOULD 
   implement all the matching rules in section 8.

   Servers MAY implement additional matching rules not listed in this 
   document, and if they do so, MUST publish the definitions of the 
   matching rules in the matchingRules attribute of their 
   subschema entries. If the server supports the extensibleMatch, then 
   the server MUST publish the relationship between the matching rules
   and attributes in the matchingRuleUse attribute.

   For example, a server which implements a privately-defined matching
   rule for performing sound-alike matches on Directory String-valued 
   attributes would include the following in the subschema entry 
   (1.2.3.4.5 is an example, the OID of an actual matching rule would be 
   different):

   matchingRule: ( 1.2.3.4.5 NAME 'soundAlikeMatch' 
    SYNTAX '1.3.6.1.4.1.1466.115.121.1.15' )

   If this matching rule could be used with the attributes 2.5.4.41 and
   2.5.4.15, the following would also be present:

   matchingRuleUse: ( 1.2.3.4.5 APPLIES (2.5.4.41 $ 2.5.4.15) )

   A client could then make use of this matching rule by sending a 
   search operation in which the filter is of the extensibleMatch choice,
   the matchingRule field is "soundAlikeMatch", and the type field is 
   "2.5.4.41" of "2.5.4.15".


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5. Attribute Types

   All LDAP server implementations MUST recognize the attribute types 
   defined in this section.  These types are based on definitions in 
   X.501(93) [3].

   Servers SHOULD also recognize all the attributes from section 5 of 
   [12].

5.1. Standard Operational Attributes

   Servers MUST maintain values of these attributes in accordance with 
   the definitions in X.501(93).

5.1.1. createTimestamp

   This attribute SHOULD appear in entries which were created using 
   the Add operation.

    ( 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 ) 

5.1.2. modifyTimestamp

   This attribute SHOULD appear in entries which have been modified 
   using the Modify operation.
 
    ( 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 ) 

5.1.3. creatorsName

   This attribute SHOULD appear in entries which were created using 
   the Add operation.
 
    ( 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 ) 
 
5.1.4. modifiersName

   This attribute SHOULD appear in entries which have been modified 
   using the Modify operation.

    ( 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 ) 





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5.1.5. subschemaSubentry

   The value of this attribute is the name of a subschema entry (or
   subentry if the server is based on X.500(93)) in which the server
   makes available attributes specifying the schema. 

    ( 2.5.18.10 NAME 'subschemaSubentry' 
      EQUALITY distinguishedNameMatch 
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.12' NO-USER-MODIFICATION 
      SINGLE-VALUE USAGE directoryOperation )

5.1.6. attributeTypes

   This attribute is typically located in the subschema entry.

    ( 2.5.21.5 NAME 'attributeTypes' 
      EQUALITY objectIdentifierFirstComponentMatch
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.3' USAGE directoryOperation ) 

5.1.7. objectClasses

   This attribute is typically located in the subschema entry.

    ( 2.5.21.6 NAME 'objectClasses' 
      EQUALITY objectIdentifierFirstComponentMatch
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.37' USAGE directoryOperation ) 

5.1.8. matchingRules

   This attribute is typically located in the subschema entry.

    ( 2.5.21.4 NAME 'matchingRules' 
      EQUALITY objectIdentifierFirstComponentMatch
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.30' USAGE directoryOperation ) 

5.1.9. matchingRuleUse

   This attribute is typically located in the subschema entry.

    ( 2.5.21.8 NAME 'matchingRuleUse' 
      EQUALITY objectIdentifierFirstComponentMatch
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.31' USAGE directoryOperation ) 

5.2. LDAP Operational Attributes

   These attributes are only present in the root DSE (see [1] and [3]).

   Servers MUST recognize these attribute names, but it is not required 
   that a server provide values for these attributes, when the 
   attribute corresponds to a feature which the server does not 
   implement.





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5.2.1. namingContexts

   The values of this attribute correspond to naming contexts which this
   server masters or shadows.  If the server does not master 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 contains 
   the entire directory, the attribute will have a single value, and 
   that value will be the empty string (indicating the null DN of the 
   root). This attribute will allow a client to choose suitable base 
   objects for searching when it has contacted a server.

    ( 1.3.6.1.4.1.1466.101.120.5 NAME 'namingContexts'
     SYNTAX '1.3.6.1.4.1.1466.115.121.1.12' USAGE dSAOperation )

5.2.2. altServer

   The values of this attribute are URLs of other servers which may be 
   contacted when this server becomes unavailable.  If the server does 
   not know of any other servers which could be used this attribute 
   will be absent. Clients may cache this information in case their 
   preferred LDAP server later becomes unavailable.

    ( 1.3.6.1.4.1.1466.101.120.6 NAME 'altServer'
     SYNTAX '1.3.6.1.4.1.1466.115.121.1.26' USAGE dSAOperation )

5.2.3. supportedExtension

   The values of this attribute are OBJECT IDENTIFIERs identifying the 
   supported extended operations which the server supports.   

   If the server does not support any extensions this attribute will be 
   absent.

    ( 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 )

5.2.4. supportedControl

   The values of this attribute are the OBJECT IDENTIFIERS identifying 
   controls which the server supports.  If the server does not 
   support any controls, this attribute will be absent.

    ( 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 )

5.2.5. supportedSASLMechanisms

   The values of this attribute are the names of supported SASL
   mechanisms which the server supports.  If the server does not 
   support any mechanisms this attribute will be absent.

    ( 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 )



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5.2.6. supportedLDAPVersion

   The values of this attribute are the versions of the LDAP protocol 
   which the server implements.

    ( 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 )

5.3. LDAP Subschema Attribute

   This attribute is typically located in the subschema entry.

5.3.1. ldapSyntaxes

   Servers MAY use this attribute to list the syntaxes which are 
   implemented.  Each value corresponds to one syntax. 

    ( 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 )

6. Syntaxes

   Servers SHOULD recognize all the syntaxes described in this section. 
   Each syntax begins with a sample value of the ldapSyntaxes attribute
   which defines the OBJECT IDENTIFIER of the syntax.  The descriptions
   of syntax names are not carried in protocol, and are not guaranteed
   to be unique.

6.1. Attribute Type Description

   ( 1.3.6.1.4.1.1466.115.121.1.3 DESC 'Attribute Type Description' )

   Values in this syntax are encoded according to the BNF given at the
   start of section 4.2. For example,

        ( 2.5.4.0 NAME 'objectClass' 
          SYNTAX '1.3.6.1.4.1.1466.115.121.1.38' )

6.2. Binary

   ( 1.3.6.1.4.1.1466.115.121.1.5 DESC 'Binary' )

   Values in this syntax are encoded as described in section 4.3.1.

6.3. Bit String

   ( 1.3.6.1.4.1.1466.115.121.1.6 DESC 'Bit String' )

   Values in this syntax are encoded according to the following BNF:

      bitstring = "'" *binary-digit "'B"

      binary-digit = "0" / "1"


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   Example:
  
        '0101111101'B

6.4. Boolean

   ( 1.3.6.1.4.1.1466.115.121.1.7 DESC 'Boolean' )

   Values in this syntax are encoded according to the following BNF:

      boolean = "TRUE" / "FALSE"

   Boolean values have an encoding of "TRUE" if they are logically true,
   and have an encoding of "FALSE" otherwise.

6.5. Certificate

   ( 1.3.6.1.4.1.1466.115.121.1.8 DESC 'Certificate' )

   Because of the changes from X.509(1988) and X.509(1993) and 
   additional changes to the ASN.1 definition to support certificate 
   extensions, no string representation is defined, and values in
   this syntax MUST only be transferred using the binary encoding, by 
   requesting or returning the attributes with descriptions 
   "userCertificate;binary" or "caCertificate;binary".  The BNF notation 
   in RFC 1778 for "User Certificate" is not recommended to be used.

6.6. Certificate List

   ( 1.3.6.1.4.1.1466.115.121.1.9 DESC 'Certificate List' )

   Because of the incompatibility of the X.509(1988) and X.509(1993) 
   definitions of revocation lists, values in this syntax MUST only be 
   transferred using a binary encoding, by requesting or returning the 
   attributes with descriptions "certificateRevocationList;binary" or 
   "authorityRevocationList;binary".  The BNF notation in RFC 1778 for 
   "Authority Revocation List" is not recommended to be used.

6.7. Certificate Pair

   ( 1.3.6.1.4.1.1466.115.121.1.10 DESC 'Certificate Pair' )

   Because the Certificate is being carried in binary, values in this 
   syntax MUST only be transferred using a binary encoding, by requesting 
   or returning the attribute description "crossCertificatePair;binary". 
   The BNF notation in RFC 1778 for "Certificate Pair" is not 
   recommended to be used.

6.8. Country String

   ( 1.3.6.1.4.1.1466.115.121.1.11 DESC 'Country String' )

   A value in this syntax is encoded the same as a value of 
   Directory String syntax.  Note that this syntax is limited to values 
   of exactly two printable string characters.

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      CountryString  = p p

   Example:
      US

6.9. DN

   ( 1.3.6.1.4.1.1466.115.121.1.12 DESC 'DN' )

   Values in the Distinguished Name syntax are encoded to have the
   representation defined in [5].  Note that this representation is not 
   reversible to an ASN.1 encoding used in X.500 for Distinguished 
   Names, as the CHOICE of any DirectoryString element in an RDN is no 
   longer known.

   Examples (from [5]):
      CN=Steve Kille,O=Isode Limited,C=GB
      OU=Sales+CN=J. Smith,O=Widget Inc.,C=US
      CN=L. Eagle,O=Sue\, Grabbit and Runn,C=GB
      CN=Before\0DAfter,O=Test,C=GB
      1.3.6.1.4.1.1466.0=#04024869,O=Test,C=GB
      SN=Lu\C4\8Di\C4\87

6.10. Directory String

   ( 1.3.6.1.4.1.1466.115.121.1.15 DESC 'Directory String' )

   A string in this syntax is encoded in the UTF-8 form of ISO 10646 
   (a superset of Unicode).  Servers and clients MUST be prepared to 
   receive encodings of arbitrary Unicode characters, including 
   characters not presently assigned to any character set.

   For characters in the PrintableString form, the value is encoded as 
   the string value itself.

   If it is of the TeletexString form, then the characters are 
   transliterated to their equivalents in UniversalString, and encoded 
   in UTF-8 [9].

   If it is of the UniversalString or BMPString forms [10], UTF-8 is 
   used to encode them. 

   Note: the form of DirectoryString is not indicated in protocol 
   unless the attribute value is carried in binary.  Servers which 
   convert to DAP MUST choose an appropriate form.  Servers MUST NOT 
   reject values merely because they contain legal Unicode characters 
   outside of the range of printable ASCII.

   Example:
 
      This is a string of DirectoryString containing #!%#@





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6.11. DIT Content Rule Description

   ( 1.3.6.1.4.1.1466.115.121.1.16 DESC 'DIT Content Rule Description' )

   Values in this syntax are encoded according to the following BNF.
   Implementors should note that future versions of this document 
   may have expanded this BNF to include additional terms.

      DITContentRuleDescription = "("
          numericoid   ; Structural ObjectClass identifier
          [ "NAME" qdescrs ]
          [ "DESC" qdstring ]
          [ "OBSOLETE" ]
          [ "AUX" oids ]    ; Auxiliary ObjectClasses
          [ "MUST" oids ]   ; AttributeType identifiers
          [ "MAY" oids ]    ; AttributeType identifiers
          [ "NOT" oids ]    ; AttributeType identifiers
         ")"

6.12. Facsimile Telephone Number

   ( 1.3.6.1.4.1.1466.115.121.1.22 DESC 'Facsimile Telephone Number' )

   Values in this syntax are encoded according to the following BNF:

      fax-number    = printablestring [ "$" faxparameters ]

      faxparameters = faxparm / ( faxparm "$" faxparameters )

      faxparm = "twoDimensional" / "fineResolution" / 
                "unlimitedLength" /
                "b4Length" / "a3Width" / "b4Width" / "uncompressed"

   In the above, the first printablestring is the actual fax number,
   and the faxparm tokens represent fax parameters.

6.13. Fax

   ( 1.3.6.1.4.1.1466.115.121.1.23 DESC 'Fax' )

   Values in this syntax are encoded as if they were octet strings
   containing Group 3 Fax images as defined in [7].

6.14. Generalized Time

   ( 1.3.6.1.4.1.1466.115.121.1.24 DESC 'Generalized Time' )

   Values in this syntax are encoded as printable strings, represented 
   as specified in X.208.  Note that the time zone must be specified.
   It is strongly recommended that GMT time be used.  For example,

                199412161032Z




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6.15. IA5 String

   ( 1.3.6.1.4.1.1466.115.121.1.26 DESC 'IA5 String' )

   The encoding of a value in this syntax is the string value itself.

6.16. INTEGER

   ( 1.3.6.1.4.1.1466.115.121.1.27 DESC 'INTEGER' )

   Values in this syntax are encoded as the decimal representation 
   of their values, with each decimal digit represented by the its 
   character equivalent. So the number 1321 is represented by the 
   character string "1321".

6.17. JPEG

   ( 1.3.6.1.4.1.1466.115.121.1.28 DESC 'JPEG' )

   Values in this syntax are encoded as strings containing JPEG images in 
   the JPEG File Interchange Format (JFIF), as described in [8].

6.18. Matching Rule Description

   ( 1.3.6.1.4.1.1466.115.121.1.30 DESC 'Matching Rule Description' )

   Values of type matchingRules are encoded as strings according to
   the BNF given in section 4.5. 

6.19. Matching Rule Use Description

   ( 1.3.6.1.4.1.1466.115.121.1.31 DESC 'Matching Rule Use Description' )

   Values of type matchingRuleUse are encoded as strings according to
   the BNF given in section 4.5.

6.20. MHS OR Address

   ( 1.3.6.1.4.1.1466.115.121.1.33 DESC 'MHS OR Address' )

   Values in this syntax are encoded as strings, according to the format 
   defined in [11].

6.21. Name And Optional UID

   ( 1.3.6.1.4.1.1466.115.121.1.34 DESC 'Name And Optional UID' )

   Values in this syntax are encoded according to the following BNF:

      NameAndOptionalUID = DistinguishedName [ "#" bitstring ]

   Although the '#' character may occur in a string representation of a 
   distinguished name, no additional special quoting is done.

   This syntax has been added subsequent to RFC 1778.

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   Example:

      1.3.6.1.4.1.1466.0=#04024869,O=Test,C=GB#'0101'B

6.22. Name Form Description

   ( 1.3.6.1.4.1.1466.115.121.1.35 DESC 'Name Form Description' )

   Values in this syntax are encoded according to the following BNF.
   Implementors should note that future versions of this document 
   may have expanded this BNF to include additional terms.

      NameFormDescription = "(" whsp
          numericoid whsp  ; NameForm identifier
          [ "NAME" qdescrs ]
          [ "DESC" qdstring ]
          [ "OBSOLETE" whsp ]
          "OC" woid         ; Structural ObjectClass
          "MUST" oids       ; AttributeTypes
          [ "MAY" oids ]    ; AttributeTypes
      whsp ")"

6.23. Numeric String

   ( 1.3.6.1.4.1.1466.115.121.1.36 DESC 'Numeric String' )

   The encoding of a string in this syntax is the string value itself. 
   Example:
  
      1997

6.24. Object Class Description

   ( 1.3.6.1.4.1.1466.115.121.1.37 DESC 'Object Class Description' )

   Values in this syntax are encoded according to the BNF in section 4.4.

6.25. OID

   ( 1.3.6.1.4.1.1466.115.121.1.38 DESC 'OID' )

   Values in the Object Identifier syntax are encoded according to 
   the BNF in section 4.1 for "oid".

   Example:

       1.2.3.4
       cn








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6.26. Other Mailbox

   ( 1.3.6.1.4.1.1466.115.121.1.39 DESC 'Other Mailbox' )

   Values in this syntax are encoded according to the following BNF:

      otherMailbox = mailbox-type "$" mailbox

      mailbox-type = printablestring

      mailbox = 

   In the above, mailbox-type represents the type of mail system in
   which the mailbox resides, for example "MCIMail"; and mailbox is 
   the actual mailbox in the mail system defined by mailbox-type.

6.27. Postal Address

   ( 1.3.6.1.4.1.1466.115.121.1.41 DESC 'Postal Address' )

   Values in this syntax are encoded according to the following BNF:

      postal-address = dstring *( "$" dstring )

   In the above, each dstring component of a postal address value is
   encoded as a value of type Directory String syntax.  Backslashes and 
   dollar characters, if they occur in the component, are quoted as 
   described in section 4. 

   Example:

      1234 Main St.$Anytown, CA 12345$USA
      \241,000,000 Sweepstakes$PO Box 1000000$Anytown, CA 12345$USA

6.28. Presentation Address

   ( 1.3.6.1.4.1.1466.115.121.1.43 DESC 'Presentation Address' )

   Values in this syntax are encoded with the representation described
   in RFC 1278 [6].

6.29. Printable String

   ( 1.3.6.1.4.1.1466.115.121.1.44 DESC 'Printable String' )

   The encoding of a value in this syntax is the string value itself.  
   PrintableString is limited to the characters in production p of 
   section 4.1.

   Example:
 
      This is a PrintableString




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6.30. Telephone Number

   ( 1.3.6.1.4.1.1466.115.121.1.50 DESC 'Telephone Number' )

   Values in this syntax are encoded as if they were Printable String 
   types.  Telephone numbers are recommended in X.520 to be in 
   international form.  

   Example:
 
      +1 512 305 0280

6.31. UTC Time

   ( 1.3.6.1.4.1.1466.115.121.1.53 DESC 'UTC Time' )

   Values in this syntax are encoded as if they were printable
   strings with the strings containing a UTCTime value.  This is 
   historical; new attribute definitions SHOULD use GeneralizedTime 
   instead.

6.32. LDAP Syntax Description

   ( 1.3.6.1.4.1.1466.115.121.1.54 DESC 'LDAP Syntax Description' )

   Values in this syntax are encoded according to the BNF in section
   4.3.3.

7. Object Classes

   Servers SHOULD recognize all the names of standard classes from 
   section 7 of [12].

7.1. Extensible Object Class

   The extensibleObject object class, if present in an entry, permits 
   that entry to optionally hold any attribute.  The MAY attribute list 
   of this class is implicitly the set of all attributes.

    ( 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. 

   Note that not all servers will implement this object class, and those
   which do not will reject requests to add entries which contain this 
   object class, or modify an entry to add this object class.








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8. Matching Rules

   Servers which implement the extensibleMatch filter SHOULD allow 
   all the matching rules listed in this section to be used in the 
   extensibleMatch.  In general these servers SHOULD allow matching 
   rules to be used with all attribute types known to the server, when
   the assertion syntax of the matching rule is the same as the value 
   syntax of the attribute.

   Servers MAY implement additional matching rules. 

8.1. Matching Rules used in Equality Filters

   Servers SHOULD be capable of performing the following matching rules.

   For all these rules, the assertion syntax is the same as the value 
   syntax.

    ( 2.5.13.0 NAME 'objectIdentifierMatch' 
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.38' )

   If the client supplies a filter using an objectIdentifierMatch whose 
   matchValue oid is in the "descr" form, and the oid is not recognized 
   by the server, then the filter is Undefined. 

    ( 2.5.13.1 NAME 'distinguishedNameMatch' 
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.12' )

    ( 2.5.13.2 NAME 'caseIgnoreMatch' 
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.15' )

    ( 2.5.13.8 NAME 'numericStringMatch' 
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.36' )

    ( 2.5.13.11 NAME 'caseIgnoreListMatch' 
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.41' )

    ( 2.5.13.14 NAME 'integerMatch' 
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.27' )

    ( 2.5.13.16 NAME 'bitStringMatch' 
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.6' )

    ( 2.5.13.20 NAME 'telephoneNumberMatch' 
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.50' )

    ( 2.5.13.22 NAME 'presentationAddressMatch' 
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.43' )

    ( 2.5.13.23 NAME 'uniqueMemberMatch' 
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.34' )

    ( 2.5.13.24 NAME 'protocolInformationMatch'
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.42' )


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    ( 2.5.13.27 NAME 'generalizedTimeMatch' 
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.24' )

    ( 1.3.6.1.4.1.1466.109.114.1 NAME 'caseExactIA5Match' 
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.26' )

    ( 1.3.6.1.4.1.1466.109.114.2 NAME 'caseIgnoreIA5Match' 
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.26' )

   When performing the caseIgnoreMatch, caseIgnoreListMatch, 
   telephoneNumberMatch, caseExactIA5Match and caseIgnoreIA5Match,
   multiple adjoining whitespace characters are treated the same as an 
   individual space, and leading and trailing whitespace is ignored.

   Clients MUST NOT assume that servers are capable of transliteration
   of Unicode values.

8.2. Matching Rules used in Inequality Filters

   Servers SHOULD be capable of performing the following matching rules,
   which are used in greaterOrEqual and lessOrEqual filters.

    ( 2.5.13.28 NAME 'generalizedTimeOrderingMatch'
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.24' )

    ( 2.5.13.3 NAME 'caseIgnoreOrderingMatch' 
      SYNTAX '1.3.6.1.4.1.1466.115.121.1.15' )

   The sort ordering for a caseIgnoreOrderingMatch is
   implementation-dependent.

8.3. Matching Rules for Subschema Attributes

   Servers which allow subschema entries to be modified by clients MUST 
   support the following matching rule, as it is the equality matching
   rule for several of the subschema attributes. 

   ( 2.5.13.30 NAME 'objectIdentifierFirstComponentMatch'
     SYNTAX '1.3.6.1.4.1.1466.115.121.1.38' )

   Implementors should note that the assertion syntax of this matching 
   rule, an OID, is different from the value syntax of attributes for 
   which this is the equality matching rule.

   If the client supplies a filter using an 
   objectIdentifierFirstComponentMatch whose matchValue oid is in the 
   "descr" form, and the oid is not recognized by the server, then the 
   filter is Undefined. 








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9. Security Considerations

9.1. Disclosure

   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.

9.2. Use of Attribute Values in Security Applications

   The transformations of an AttributeValue value from its X.501 form to
   an LDAP string representation are not always reversible back to the 
   same BER or DER form.  An example of a situation which requires the 
   DER form of a distinguished name is the verification of an X.509 
   certificate.

   For example, a distinguished name consisting of one RDN with one AVA,
   in which the type is commonName and the value is of the TeletexString 
   choice with the letters 'Sam' would be represented in LDAP as the
   string CN=Sam.  Another distinguished name in which the value is 
   still 'Sam' but of the PrintableString choice would have the same 
   representation CN=Sam.

   Applications which require the reconstruction of the DER form of the 
   value SHOULD NOT use the string representation of attribute syntaxes
   when converting a value to LDAP format.  Instead it SHOULD use the 
   Binary syntax.

10. Acknowledgements

   This document is based substantially on RFC 1778, written by Tim 
   Howes, Steve Kille, Wengyik Yeong and Colin Robbins.

   Many of the attribute syntax encodings defined in this and 
   related documents are adapted from those used in the QUIPU and the 
   IC R3 X.500 implementations. The contributions of the authors of both 
   these implementations in the specification of syntaxes are gratefully 
   acknowledged.

11. Authors Addresses

       Mark Wahl
       Critical Angle Inc.
       4815 West Braker Lane #502-385
       Austin, TX 78759
       USA

       Phone:  +1 512 372-3160
       EMail:  M.Wahl@critical-angle.com






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       Andy Coulbeck
       Isode Inc.
       3925 West Braker Lane #333
       Austin, TX 78759 
       USA

       Phone:  +1 512 305-0280
       EMail:  A.Coulbeck@isode.com

       Tim Howes
       Netscape Communications Corp.
       501 E. Middlefield Rd
       Mountain View, CA 94043
       USA
       
       Phone:  +1 415 254-1900
       EMail:   howes@netscape.com

       Steve Kille
       Isode Limited
       The Dome, The Square
       Richmond
       TW9 1DT
       UK

       Phone:  +44-181-332-9091
       EMail:  S.Kille@isode.com

12. Bibliography

   [1] M. Wahl, T. Howes, S. Kille, "Lightweight Directory Access 
       Protocol (Version 3)", INTERNET-DRAFT 
       <draft-ietf-asid-ldapv3-protocol-06.txt>, July 1997.
 
   [2] The Directory: Selected Attribute Types.  ITU-T Recommendation 
       X.520, 1993.

   [3] The Directory: Models. ITU-T Recommendation X.501, 1993.

   [4] S. Bradner, "Key words for use in RFCs to Indicate Requirement 
       Levels", RFC 2119.
   
   [5] M. Wahl, S. Kille, "A UTF-8 String Representation of 
       Distinguished Names", INTERNET-DRAFT 
       , April 1997.

   [6] S. Kille, "A String Representation for Presentation Addresses",
       RFC 1278, University College London, November 1991.

   [7] Terminal Equipment and Protocols for Telematic Services -
       Standardization of Group 3 facsimile apparatus for document
       transmission.  CCITT, Recommendation T.4.

   [8] JPEG File Interchange Format (Version 1.02).  Eric Hamilton, 
       C-Cube Microsystems, Milpitas, CA, September 1, 1992.

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INTERNET-DRAFT    draft-ietf-asid-ldapv3-attributes-06.txt   July 1997

   [9] F. Yergeau, "UTF-8, a transformation format of Unicode and ISO 
       10646", RFC 2044, October 1996.

   [10] Universal Multiple-Octet Coded Character Set (UCS) - 
        Architecture and Basic Multilingual Plane, ISO/IEC 10646-1 : 
        1993 (With amendments).

   [11] S. Hardcastle-Kille, "Mapping between X.400(1988) / ISO 10021 
        and RFC 822", RFC 1327, May 1992.

   [12] M. Wahl, "X.500(96) User Schema for use with LDAP", 
        INTERNET-DRAFT ,
        July 1997.

   [13] D. Crocker, "Standard of the Format of ARPA-Internet Text
        Messages", STD 11, RFC 822, August 1982.






































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