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Network Working Group                                            M. WahlRequest for Comments: 2596                  Innosoft International, Inc.Category: Standards Track                                       T. Howes                                           Netscape Communications Corp.                                                                May 1999Use of Language Codes in LDAPStatus 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 inRFC 2119 [4].2. Language CodesSection 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 inRFC 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 inRFC 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 19993.2. 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 entryWahl & 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: Softwareprodukte3.6. 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 19993.8. 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 referencesRFC 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",RFC1766, 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 19998. 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.comWahl & Howes                Standards Track                     [Page 8]

RFC 2596             Use of Language Codes in LDAP              May 1999Full 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]