INTERNET-DRAFT Editor: Kurt D. Zeilenga Intended Category: Standard Track OpenLDAP Foundation Expires: 13 May 2002 13 November 2001 Obsoletes: RFC 2596 Language Tags and Ranges in LDAP draft-zeilenga-ldap-rfc2596-00.txt Status of Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. This document is intended to be, after appropriate review and revision, submitted to the RFC Editor as a Standard Track document. Distribution of this memo is unlimited. Technical discussion of this document will take place on the IETF LDAP Extensions Working Group (LDAPext) mailing list . Please send editorial comments directly to the document editor . 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.'' The list of current Internet-Drafts can be accessed at . The list of Internet-Draft Shadow Directories can be accessed at . Copyright 2001, The Internet Society. All Rights Reserved. Please see the Copyright section near the end of this document for more information. Abstract This document details the use of Language Tags and Ranges in LDAP. This document replaces RFC 2596. Zeilenga Language Tags and Ranges in LDAP [Page 1] INTERNET-DRAFT draft-zeilenga-ldap-rfc2596-00.txt 13 November 2001 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]. 1. Background and Intended Use The Lightweight Directory Access Protocol (LDAP) [LDAPTS] 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 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 tags and ranges [RFC3066] are carried in LDAP and are to be interpreted by LDAP implementations. All implementations MUST be prepared to accept language tags and ranges in the LDAP protocol. This document replaces RFC 2596. Appendix A summaries changes made since RFC 2596. The remainder of this section provides a summary of Langauge Tags, Language Ranges, and Attribute Descriptions. 1.1. Language Tags Section 2 of BCP 47 [RFC3066] describes the language tag 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". Language tags are case insensitive. For example, the language tag "en-us" is the same as "EN-US". Section 2 of this document details use of language tags in LDAP. 1.2. Language Ranges Section 2.5 of BCP 47 [RFC3066] describes the language ranges. Language ranges are used to specify sets of language tags. A language range matches a language tag if it exactly equals the tag, or if it exactly equals a prefix of the tag such that the first character following the prefix is "-". The special tag "*" matches Zeilenga Language Tags and Ranges in LDAP [Page 2] INTERNET-DRAFT draft-zeilenga-ldap-rfc2596-00.txt 13 November 2001 all tags. Due to restrictions upon option naming in LDAP, this document uses a different language range syntax. However, the semantics of language ranges in LDAP is consistent with BCP 47. Section 3 of this document details use of language ranges in LDAP. 1.3. Attribute Descriptions An attribute consists of a type, a list of "subtyping" (or "tag") options for that type, and a set of one or more values. The type and the options are combined into the AttributeDescription, defined in section 4.1.5 of RFC 2251 [RFC2251]. AttributeDescription may also contain options which are not part of the attribute, but indicate some function such as the transfer encoding. In summary, an attribute with "subtyping" (or "tag") options is treated as a subtype of the attribute without the options. If a server does not support any of the options, the attribute is treated as an unrecognized attribute. As language tags are intended to stored with the attribute, they are to treated as "subtyping" (or "tag") options. Language range are used only to match against language ranges and are not stored with the attribute, they are not treated "subtyping" (or "tag") options but as detailed in Section 3 of this document. 2. Use of Language Tags in LDAP This section describes how LDAP implementations MUST interpret language tags in performing operations. Servers which support storing attributes with language tag in the DIT SHOULD allow any attribute type it recognizes that has the Directory String syntax to have language tag options associated with it. Servers MAY allow language options to be associated with other attributes types. Clients SHOULD NOT assume servers are capable of storing attributes with language tags in the directory. Implementations MUST NOT otherwise interpret the structure of the tag when comparing two tag, and MUST treat them as simply strings of characters. Implementations MUST allow any arbitrary string which conforms to the syntax defined in BCP 47 to be used as a language tag. Zeilenga Language Tags and Ranges in LDAP [Page 3] INTERNET-DRAFT draft-zeilenga-ldap-rfc2596-00.txt 13 November 2001 2.1. Language Tag Options A language tag option associates a natural language with values for that attribute. An attribute description may contain multiple language tag options. An entry may contain multiple attributes with same attribute type but different language tag (and other) options. A language tag option conforms to the following ABNF [RFC2234]: language-tag-option = "lang-" Language-Tag where the Language-Tag production is as defined in BCP 47 [RFC3066]. A language tag option is a "subtyping" (or "tag") option [RFC2251bis]. A language tag option has no effect on the tranfer encoding nor on the syntax of the attribute values. Examples of valid AttributeDescription: givenName;lang-en-US CN;lang-ja SN;lang-de;lang-gem-PFL O;lang-i-klingon;x-foobar description;x-foobar CN Notes: The last two have no language tag options. The x-foobar option is fictious and used for example purposes. 2.2. Search Filter If langugage tag options are present in an AttributeDescription in an assertion, then for each entry within scope, the values of each attribute whose AttributeDescription consists of the same attribute type or its subtypes and contains each of the presented (and possibly other) options is to be matched. 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 dn: SN=Ray,DC=example,DC=com 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 Zeilenga Language Tags and Ranges in LDAP [Page 4] INTERNET-DRAFT draft-zeilenga-ldap-rfc2596-00.txt 13 November 2001 CN;lang-en-US;x-foobar: Billy Ray MATCHES CN;lang-en;x-foobar: Billy Ray DOES NOT MATCH (differing lang-) CN;x-foobar: Billy Ray DOES NOT MATCH (no lang-) name: Billy Ray DOES NOT MATCH (no lang-) SN;lang-en-GB;lang-en-US: Billy Ray MATCHES 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 tag option in a search filter AttributeDescription will often filter out desirable values where the tag 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 attributes with language tag options in the DIT, then any assertion which includes a language tag option will not 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 assertions to Undefined. If no options are specified in the assertion, 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 dn: SN=Ray,DC=example,DC=net 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;x-foobar: Billy Ray MATCHES CN;lang-en;x-foobar: Billy Ray MATCHES CN;x-foobar: Billy Ray MATCHES name: Billy Ray MATCHES SN;lang-en-GB;lang-en-US: Billy Ray MATCHES SN: Ray DOES NOT MATCH (wrong value) 2.3. Requested Attributes in Search Clients can provide language tag options in AttributeDescription in the requested attribute list in a search request. If language tag options are provided in an attribute description, then only attributes in a directory entry whose attribute descriptions have Zeilenga Language Tags and Ranges in LDAP [Page 5] INTERNET-DRAFT draft-zeilenga-ldap-rfc2596-00.txt 13 November 2001 the same attribute type or its subtype and the provided language tags options are to be returned. Thus if a client requests just the attribute "name;lang-en", the server would return "name;lang-en" and "CN;lang-en;lang-ja" but not "SN" nor "name;lang-fr". Clients can provide in the attribute list multiple AttributeDescription which have the same base attribute type but different options. For example a client could provide both "name;lang-en" and "name;lang-fr", and this would permit an attribute with either language tag option 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 attributes with language tag options in the DIT, then any attribute descriptions in the list which include language tag options 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 tag option, then all attribute values regardless of their language tag option are returned. For example, if the client requests a "description" attribute, and a matching entry contains the following attributes: 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 would return: description: software description;lang-en: software products description;lang-de: Softwareprodukte 2.4. Compare Language tag options 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 tag options in a search filter with an equality match, as described in section 2.2. If there is no attribute in the entry with the same subtype and language tag options, Zeilenga Language Tags and Ranges in LDAP [Page 6] INTERNET-DRAFT draft-zeilenga-ldap-rfc2596-00.txt 13 November 2001 the noSuchAttributeType error will be returned. Thus for example a compare request of type "name" and assertion value "Johann", against an entry containing the following attributes: objectclass: top objectclass: person givenName;lang-de-DE: Johann CN: Johann Sibelius SN: Sibelius would 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 attributes with language tag options in the DIT, then any comparison which includes a language tag option will always fail to locate an attribute, and noSuchAttributeType will be returned. 2.5. Add Operation Clients can provide language options in AttributeDescription in attributes of a new entry to be created. A client can provide multiple attributes with the same attribute type and value, so long as each attribute has a different set of language tag options. For example, the following is a legal request. dn: CN=John Smith,DC=example,DC=com objectclass: top objectclass: person objectclass: residentialPerson name: John Smith CN: John Smith CN;lang-en: John Smith SN: Smith SN;lang-en;lang-en-US: Smith streetAddress: 1 University Street streetAddress;lang-en: 1 University Street streetAddress;lang-fr: 1 rue Universite houseIdentifier;lang-fr: 9e etage Zeilenga Language Tags and Ranges in LDAP [Page 7] INTERNET-DRAFT draft-zeilenga-ldap-rfc2596-00.txt 13 November 2001 If a server does not support storing language tag options with attribute values in the DIT, then it MUST treat an AttributeDescription with a language tag option as an unrecognized attribute. If the server forbids the addition of unrecognized attributes then it MUST fail the add request with an appropriate result code. 2.6. Modify Operation A client can provide language tag options in an AttributeDescription as part of a modification element in the modify operation. Attribute types and language tag options 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 language tag options, then those language tag options MUST be provided in the modify operation, and if the stored values to be deleted do not have any language tag option, then no language tag option is to be provided. If the server does not support storing language tag options with attribute values in the DIT, then it MUST treat an AttributeDescription with a language tag option as an unrecognized attribute, and MUST fail the request with an appropriate result code. 3. Use of Language Ranges in LDAP Since the publication of RFC 2596, it has become apparent that there is a need to provide a mechanism for a client to request attributes based upon set of language tag options whose tags all begin with the same sequence of subtags. AttributeDescriptions containing language range options are intended to be used in attribute value assertions, search attribute lists, and other places where the client desires to provide an attribute description matching of a range of language tags associated with attributes. A language range option conforms to the following ABNF [RFC 2234]: language-range-option = "lang-" [ Language-Tag "-" ] where the Language-Tag production is as defined in BCP 47 [RFC3066]. A language range option matches a langugage tag option if language range option less the trailing "-" matches exactly the language tag or Zeilenga Language Tags and Ranges in LDAP [Page 8] INTERNET-DRAFT draft-zeilenga-ldap-rfc2596-00.txt 13 November 2001 if the language range option (including the trailing "-") matches a prefix of the language tag option. Note that the language range option "lang-" matches all language tag options. Examples of valid AttributeDescription containing language range options: givenName;lang-en- CN;lang- O;lang-x-;x-foobar A language range option is not a "subtyping" (or "tag") option [RFC2251bis]. Attributes cannot be stored with language range options. Any attempt to add or update an attribute description with a languague range option SHALL be treated as an undefined attribute type and result in an error. A language range option has no effect on the tranfer encoding nor on the syntax of the attribute values. Servers SHOULD support assertion of language ranges for any attribute which they allow to stored with language tags. 3.1. Search Filter If a langugage range option is present in an AttributeDescription in an assertion, then for each entry within scope, the values of each attribute whose AttributeDescription consists of the same attribute type or its subtypes and contains a language tag option matching the language range option are to be returned. Thus for example a filter of an equality match of type "name;lang-en-" and assertion value "Billy Ray", against the following directory entry dn: SN=Ray,DC=example,DC=com 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;x-foobar: Billy Ray MATCHES CN;lang-en;x-foobar: Billy Ray MATCHES CN;x-foobar: Billy Ray DOES NOT MATCH (no lang-) name: Billy Ray DOES NOT MATCH (no lang-) SN;lang-en-GB;lang-en-US: Billy Ray MATCHES SN: Ray DOES NOT MATCH (wrong value) Zeilenga Language Tags and Ranges in LDAP [Page 9] INTERNET-DRAFT draft-zeilenga-ldap-rfc2596-00.txt 13 November 2001 (Note that "CN" and "SN" are subtypes of "name".) If the server does not support storing attributes with language tag options in the DIT, then any assertion which includes a language range option will not 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 assertions to Undefined. 3.2. Requested Attributes in Search Clients can provide language range options in AttributeDescription in the requested attribute list in a search request. If a language range option is provided in an attribute description, then only attributes in a directory entry whose attribute descriptions have the same attribute type or its subtype and a language tag option matching the provided language range option are to be returned. Thus if a client requests just the attribute "name;lang-en-", the server would return "name;lang-en-US" and "CN;lang-en;lang-ja" but not "SN" nor "name;lang-fr". Clients can provide in the attribute list multiple AttributeDescription which have the same base attribute type but different options. For example a client could provide both "name;lang-en-" and "name;lang-fr-", and this would permit an attribute whose type was name or subtype of name and with a language tag option matching either language range option to be returned. If a server does not support storing attributes with language tag options in the DIT, then any attribute descriptions in the list which include language range options are to be ignored, just as if they were unknown attribute types. 3.3. Compare Language range options 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 range options in a search filter with an equality match, as described in section 3.1. If there is no attribute in the entry with the same subtype and a matching language tag option, the noSuchAttributeType error will be returned. Thus for example a compare request of type "name;lang-" and assertion value "Johann", against the entry with the following attributes: objectclass: top Zeilenga Language Tags and Ranges in LDAP [Page 10] INTERNET-DRAFT draft-zeilenga-ldap-rfc2596-00.txt 13 November 2001 objectclass: person givenName;lang-de-DE: Johann CN: Johann Sibelius SN: Sibelius will cause the server to return compareTrue. (Note that the language range option "lang-" matches any language tag option.) However, if the client issued a compare request of type "name;lang-de" and assertion value "Sibelius" against the above entry, the request would fail with the noSuchAttributeType error. If the server does not support storing attributes with language tag options in the DIT, then any comparison which includes a language range option will always fail to locate an attribute, and noSuchAttributeType will be returned. 4. Discovering Language Option Support A server SHOULD indicate that it supports storing attributes with language tag options in the DIT by publishing OID.TDB as a value of the supportedFeatures [FEATURES] attribute in the root DSE. A server SHOULD indicate that it supports language range matching of attributes with language tag options stored in the DIT by publishing OID.TDB as a value of the supportedFeatures [FEATURES] attribute in the root DSE. A server MAY restrict use of language tag options to a subset of the attribute types it recongizes. This document does not define a mechanism for determining which subset of attribute types can be used with language tag options. 5. Security Considerations There are no known security considerations for this document. See the security considerations sections of [LDAPTS] for security considerations of LDAP in general. 6. Acknowledgements This document is a revision of RFC 2596 by Mark Wahl and Tim Howes. RFC 2596 was a product of the IETF ASID and LDAPEXT working groups. This document borrows from a number of IETF documents including BCP Zeilenga Language Tags and Ranges in LDAP [Page 11] INTERNET-DRAFT draft-zeilenga-ldap-rfc2596-00.txt 13 November 2001 47. 7. References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14 (also RFC 2119), March 1997. [RFC2234] D. Crocker, P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. [RFC2251] Wahl, M., Howes, T. and S. Kille, "Lightweight Directory Access Protocol (v3)", RFC 2251, December 1997. [RFC2251bis] Sermersheim, J., "Lightweight Directory Access Protocol (v3)", draft-ietf-ldapbis-protocol-xx.txt (a work in progress). [RFC3066] Alvestrand, H., "Tags for the Identification of Languages", BCP 47 (also RFC 3066), January 2001. [LDAPTS] J. Hodges, R.L. Morgan, "Lightweight Directory Access Protocol (v3): Technical Specification", draft-ietf-ldapbis-ldapv3-ts-00.txt (a work in progress). [FEATURES] K. Zeilenga, "Feature Discovery in LDAP", draft-zeilenga-ldap-features-xx.txt (a work in progress). A. Differences from RFC 2596 This document adds support for language ranges, provides a mechansism that a client can use to discover whether a server supports language tags, and clarifies how attributes with multiple language tags are to be treated. This document is a significant rewrite of RFC 2596. B. Differences from X.500(1997) X.500(1997) defines a different mechanism, contexts, as the means of representing language tags (codes). 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 BCP 47 [RFC3066], which allows for IANA registration of new tags as well as unregistered tags. c) LDAP supports language ranges. Zeilenga Language Tags and Ranges in LDAP [Page 12] INTERNET-DRAFT draft-zeilenga-ldap-rfc2596-00.txt 13 November 2001 d) LDAP does not allow language tags (and ranges) in distinguished names. e) X.500 describes subschema administration procedures to allow language codes to be associated with particular attributes types. Copyright 2001, The Internet Society. 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 AUTHORS, THE INTERNET SOCIETY, AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Zeilenga Language Tags and Ranges in LDAP [Page 13]