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rfc:rfc2596

Network Working Group M. Wahl Request for Comments: 2596 Innosoft International, Inc. Category: Standards Track T. Howes

                                         Netscape Communications Corp.
                                                              May 1999
                   Use of Language Codes in LDAP

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 (1999).  All Rights Reserved.

1. Abstract

 The Lightweight Directory Access Protocol [1] provides a means for
 clients to interrogate and modify information stored in a distributed
 directory system.  The information in the directory is maintained as
 attributes [2] of entries.  Most of these attributes have syntaxes
 which are human-readable strings, and it is desirable to be able to
 indicate the natural language associated with attribute values.
 This document describes how language codes [3] are carried in LDAP
 and are to be interpreted by LDAP servers.  All implementations MUST
 be prepared to accept language codes in the LDAP protocols.  Servers
 may or may not be capable of storing attributes with language codes
 in the directory.  This document does not specify how to determine
 whether particular attributes can or cannot have language codes.
 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].

2. Language Codes

 Section 2 of RFC 1766 [3] describes the language code format which is
 used in LDAP.  Briefly, it is a string of ASCII alphabetic characters
 and hyphens.  Examples include "fr", "en-US" and "ja-JP".

Wahl & Howes Standards Track [Page 1] RFC 2596 Use of Language Codes in LDAP May 1999

 Language codes are case insensitive.  For example, the language code
 "en-us" is the same as "EN-US" and "en-US".
 Implementations MUST NOT otherwise interpret the structure of the
 code when comparing two codes, and MUST treat them as simply strings
 of characters. Client and server implementations MUST allow any
 arbitrary string which follows the patterns given in RFC 1766 to be
 used as a language code.

3. Use of Language Codes in LDAP

 This section describes how LDAP implementations MUST interpret
 language codes in performing operations.
 In general, an attribute with a language code is to be treated as a
 subtype of the attribute without a language code.  If a server does
 not support storing language codes with attribute values in the DIT,
 then it MUST always treat an attribute with a language code as an
 unrecognized attribute.

3.1. Attribute Description

 An attribute consists of a type, a list of options for that type, and
 a set of one or more values.  In LDAP, the type and the options are
 combined into the AttributeDescription, defined in section 4.1.5 of
 [1]. This is represented as an attribute type name and a possibly-
 empty list of options.  One of these options associates a natural
 language with values for that attribute.
      language-option = "lang-" lang-code
      lang-code = printable-ascii ; a code as defined in RFC 1766
 Multiple language options may be present on a particular value.
 The language code has no effect on the character set encoding for
 string representations of DirectoryString syntax values; the UTF-8
 representation of UniversalString (ISO 10646) is always used.
 Examples of valid AttributeDescription:
      givenName;lang-en-US
      CN;lang-ja
 In LDAP and in examples in this document, a directory attribute is
 represented as an AttributeDescription with a list of values.  Note
 that the data could be stored in the LDAP server in a different
 representation.

Wahl & Howes Standards Track [Page 2] RFC 2596 Use of Language Codes in LDAP May 1999

3.2. Distinguished Names and Relative Distinguished Names

 No attribute description options are permitted in Distinguished Names
 or Relative Distinguished Names.  Thus language codes MUST NOT be
 used in forming DNs.

3.3. Search Filter

 If a language code is present in an AttributeDescription in a search
 filter, then only attribute values in the directory which match the
 base attribute type or its subtype, the language code and the
 assertion value match this filter.
 Thus for example a filter of an equality match of type "name;lang-
 en-US" and assertion value "Billy Ray", against the following
 directory entry
 objectclass: top                     DOES NOT MATCH (wrong type)
 objectclass: person                  DOES NOT MATCH (wrong type)
 name;lang-EN-US: Billy Ray           MATCHES
 name;lang-EN-US: Billy Bob           DOES NOT MATCH (wrong value)
 CN;lang-en-us: Billy Ray                MATCHES
 CN;lang-EN-US;dynamic: Billy Ray     MATCHES
 CN;lang-en;dynamic: Billy Ray        DOES NOT MATCH (differing lang-)
 name: Billy Ray                      DOES NOT MATCH (no lang-)
 SN: Ray                              DOES NOT MATCH (wrong value)
 (Note that "CN" and "SN" are subtypes of "name".)
 Client implementors should however note that providing a language
 code in a search filter AttributeDescription will often filter out
 desirable values where the language code does not match exactly.  For
 example, the filter (name;lang-en=Billy Ray) does NOT match the
 attribute "name;lang-en-US: Billy Ray".
 If the server does not support storing language codes with attribute
 values in the DIT, then any filter which includes a language code
 will always fail to match, as it is an unrecognized attribute type.
 No error would be returned because of this; a presence filter would
 evaluate to FALSE and all other forms to Undefined.
 If no language code is specified in the search filter, then only the
 base attribute type and the assertion value need match the value in
 the directory.
 Thus for example a filter of an equality match of type "name" and
 assertion value "Billy Ray", against the following directory entry

Wahl & Howes Standards Track [Page 3] RFC 2596 Use of Language Codes in LDAP May 1999

 objectclass: top                     DOES NOT MATCH (wrong type)
 objectclass: person                  DOES NOT MATCH (wrong type)
 name;lang-EN-US: Billy Ray           MATCHES
 name;lang-EN-US: Billy Bob           DOES NOT MATCH (wrong value)
 CN;lang-EN-US;dynamic: Billy Ray     MATCHES
 CN;lang-en;dynamic: Billy Ray        MATCHES
 name: Billy Ray                      MATCHES
 SN: Ray                              DOES NOT MATCH (wrong value)
 Thus in general, clients SHOULD NOT use the language code option in
 AttributeDescription fields in search filters.

3.4. Compare

 A language code can be present in an AttributeDescription used in a
 compare request AttributeValueAssertion.  This is to be treated by
 servers the same as the use of language codes in a search filter with
 an equality match, as described in the previous section.  If there is
 no attribute in the entry with the same subtype and language code,
 the noSuchAttributeType error will be returned.
 Thus for example a compare request of type "name" and assertion value
 "Johann", against an entry with all the following directory entry
 objectclass: top
 objectclass: person
 givenName;lang-de-DE: Johann
 CN: Johann Sibelius
 SN: Sibelius
 will cause the server to return compareTrue.
 However, if the client issued a compare request of type "name;lang-
 de" and assertion value "Johann" against the above entry, the request
 would fail with the noSuchAttributeType error.
 If the server does not support storing language codes with attribute
 values in the DIT, then any comparison which includes a language code
 will always fail to locate an attribute type, and noSuchAttributeType
 will be returned.
 Thus in general, clients SHOULD NOT use the language code option in
 AttributeDescription fields in the compare request.

3.5. Requested Attributes in Search

 Clients MAY provide language codes in AttributeDescription in the
 requested attribute list in a search request.

Wahl & Howes Standards Track [Page 4] RFC 2596 Use of Language Codes in LDAP May 1999

 If a language code is provided in an attribute description, then only
 attribute values in a directory entry which have the same language
 code as that provided are to be returned. Thus if a client requests
 an attribute "description;lang-en", the server MUST NOT return values
 of an attribute "description" or "description;lang-fr".
 Clients MAY provide in the attribute list multiple
 AttributeDescription which have the same base attribute type but
 different options. For example a client MAY provide both "name;lang-
 en" and "name;lang-fr", and this would permit an attribute with
 either language code to be returned.  Note there would be no need to
 provide both "name" and "name;lang-en" since all subtypes of name
 would match "name".
 If a server does not support storing language codes with attribute
 values in the DIT, then any attribute descriptions in the list which
 include language codes are to be ignored, just as if they were
 unknown attribute types.
 If a request is made specifying all attributes or an attribute is
 requested without providing a language code, then all attribute
 values regardless of their language code are returned.
 For example, if the client requests a "description" attribute, and a
 matching entry contains
 objectclass: top
 objectclass: organization
 O: Software GmbH
 description: software
 description;lang-en: software products
 description;lang-de: Softwareprodukte
 postalAddress: Berlin 8001 Germany
 postalAddress;lang-de: Berlin 8001 Deutschland
 The server will return:
 description: software
 description;lang-en: software products
 description;lang-de: Softwareprodukte

3.6. Add Operation

 Clients MAY provide language codes in AttributeDescription in
 attributes of a new entry to be created, subject to the limitation
 that the client MUST NOT use language codes in the attribute value or
 values which form the RDN of the entry.

Wahl & Howes Standards Track [Page 5] RFC 2596 Use of Language Codes in LDAP May 1999

 A client MAY provide multiple attributes with the same attribute type
 and value, so long as each attribute has a different language code,
 and at most one attribute does not have a language code option.
 Servers which support storing language codes in the DIT MUST allow
 any attribute it recognizes that has the Directory String syntax to
 have a language option associated with it. Servers SHOULD allow
 language options to be associated with other attributes.
 For example, the following is a legal request.
 objectclass: top
 objectclass: person
 objectclass: residentialPerson
 name: John Smith
 CN: John Smith
 CN;lang-en: John Smith
 SN: Smith
 streetAddress: 1 University Street
 streetAddress;lang-en: 1 University Street
 streetAddress;lang-fr: 1 rue Universite
 houseIdentifier;lang-fr: 9e etage
 If a server does not support storing language codes with attribute
 values in the DIT, then it MUST treat an AttributeDescription with a
 language code as an unrecognized attribute. If the server forbids the
 addition of unrecognized attributes then it MUST fail the add request
 with the appropriate result code.

3.7. Modify Operation

 A client MAY provide a language code in an AttributeDescription as
 part of a modification element in the modify operation.
 Attribute types and language codes MUST match exactly against values
 stored in the directory.  For example, if the modification is a
 "delete", then if the stored values to be deleted have a language
 code, the language code MUST be provided in the modify operation, and
 if the stored values to be deleted do not have a language code, then
 no language code is to be provided.
 If the server does not support storing language codes with attribute
 values in the DIT, then it MUST treat an AttributeDescription with a
 language code as an unrecognized attribute, and MUST fail the request
 with an appropriate result code.

Wahl & Howes Standards Track [Page 6] RFC 2596 Use of Language Codes in LDAP May 1999

3.8. Diagnostic Messages

 Servers SHOULD use only printable ASCII characters in the
 errorMessage field, as not all clients will be able to display the
 full range of Unicode.

4. Differences from X.500(1997)

 X.500(1997) defines a different mechanism, contexts, as the means of
 representing language tags.  This section summarizes the major
 differences in approach.
 a) An X.500 operation which has specified a language code on a value
    matches a value in the directory without a language code.
 b) LDAP references RFC 1766, which allows for IANA registration of
    new tags.
 c) LDAP does not allow language codes in distinguished names.
 d) X.500 describes subschema administration procedures to allow
    language codes to be associated with particular attributes types.

5. Security Considerations

 There are no known security considerations for this document.  See
 the security considerations sections of [1] and [2] for security
 considerations of LDAP in general.

6. Acknowledgements

 This document is a product of the IETF ASID and LDAPEXT working
 groups.  Martin Duerst provided many valuable comments on an earlier
 version of this document.

7. Bibliography

 [1] Wahl, M., Howes, T. and S. Kille, "Lightweight Directory Access
     Protocol (v3)", RFC 2251, December 1997.
 [2] Wahl, M., Coulbeck, A., Howes, T. and S. Kille, "Lightweight
     X.500 Directory Access Protocol Attribute Syntax Definitions",
     RFC 2252, December 1997.
 [3] Alvestrand, H.,"Tags for the Identification of Languages", RFC
     1766, March 1995.
 [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement
     Levels", BCP 14, RFC 2119, March 1997.

Wahl & Howes Standards Track [Page 7] RFC 2596 Use of Language Codes in LDAP May 1999

8. Authors' Addresses

 Mark Wahl
 Innosoft International, Inc.
 8911 Capital of Texas Hwy Suite 4140
 Austin, TX 78759 USA
 EMail:  M.Wahl@innosoft.com
 Tim Howes
 Netscape Communications Corp.
 501 E. Middlefield Rd
 Mountain View, CA 94043 USA
 Phone:  +1 650 937-3419
 EMail:   howes@netscape.com

Wahl & Howes Standards Track [Page 8] RFC 2596 Use of Language Codes in LDAP May 1999

Full Copyright Statement

 Copyright (C) The Internet Society (1999).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Wahl & Howes Standards Track [Page 9]

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