Network Working Group M. Wahl
INTERNET-DRAFT Critical Angle Inc.
T. Howes
Netscape Communications Corp.
Expires in six months from 6 June 1997
Intended Category: Standards Track
Use of Language Codes in LDAPv3
<draft-ietf-asid-ldapv3-lang-02.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 [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.
3. 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".
Language codes are case insensitive. For example, the language code
"en-us" is the same as "EN-US" and "en-US". One language code is a
prefix of another if both codes are equal up to the length of the
first code. For example, the language code "en" is a prefix of the
language codes "en-us" and "EN-US".
Wahl, Howes [Page 1]
INTERNET-DRAFT Use of Language Codes in LDAPv3 June 1997
Implementations MUST NOT otherwise interpret the structure of the
code when comparing two codes, but should 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.
4. 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.
Clients may request the use of a particular language through the
preferredLanguage control. This control determines how the server
interprets attributes without an explicit language parameter. The
details of this interaction for specific operations are given below.
4.1. 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
There can be at most one language option present in an
AttributeDescription.
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-JP-kanji
CN;lang-ja-JP-romaji
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 may be stored in the LDAP server in a different
representation.
Wahl, Howes [Page 2]
INTERNET-DRAFT Use of Language Codes in LDAPv3 June 1997
4.2. Preferred Language Control
The preferredLanguage control is always non-critical. Its value is
a language code as defined in RFC 1766 [3]. If this control is
absent, the default is that there is no preferred language for the
client. The OID of the control is "1.3.6.1.4.1.1466.20035".
It is recommended that clients should use the most general language
code which is suitable for their purpose. A language code with
multiple subtags may result in too much directory information being
filtered out of responses. In most cases, it is recommended that
only the primary language tag (such as "EN") should be provided.
If the server supports the storing of language codes with attribute
values in the DIT, then it MUST indicate that the OID given above is
a supported control in the supportedControl attribute of the root DSE.
Otherwise it SHOULD NOT indicate support for this control.
4.3. 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.
4.4. Search Filter
A client may provide a language code in an AttributeDescription in a
search filter. If present, 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;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".)
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
(note however than no error will be returned because of this).
Wahl, Howes [Page 3]
INTERNET-DRAFT Use of Language Codes in LDAPv3 June 1997
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
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)
There is no effect of the preferredLanguage control in filtering.
4.5. Compare
A client may provide a language code 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.
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.
There is no effect of the preferredLanguage control in comparing.
4.6. Requested Attributes in Search
Clients may provide language codes in AttributeDescription in the
requested attribute list in a search request.
Wahl, Howes [Page 4]
INTERNET-DRAFT Use of Language Codes in LDAPv3 June 1997
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 may 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, and the
preferredLanguage control has not been set, then all attribute values
regardless of their language code are returned.
For example, if the client has set no preferredLanguage control and
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: softwareproduckte
postalAddress: Berlin 8001 Germany
postalAddress;lang-de: Berlin 8001
The server will return:
description: software
description;lang-en: software products
description;lang-de: softwareproduckte
If the client has set the preferredLanguage control, then attributes
are excluded from the result if either of the following is true:
- the attribute has a language code for which the preferredLanguage
value is not a prefix, or
- the attribute does not have a language code, but there is another
attribute of the same type or a subtype in the entry, which has a
language code for which the preferredLanguage value is a prefix.
Wahl, Howes [Page 5]
INTERNET-DRAFT Use of Language Codes in LDAPv3 June 1997
For example, if the client sets that the preferredLanguage was "en"
and requests all attributes, then the following will be returned.
The "description;lang-de" and "postalAddress;lang-de" are excluded,
since the language code in these attributes does not match the
preferredLanguage. The "description" attribute is excluded, since it
is a subtype of the "description;lang-en" attribute, which does match
the language code.
objectclass: top
objectclass: organization
O: Software GmbH
description;lang-en: software products
postalAddress: Berlin 8001 Germany
If a server does not support storing language codes with attribute
values in the DIT, then it will ignore the preferredLanguage control.
4.7. 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 provide the attribute values used in the RDN
without any language code or any other option.
A client may provide multiple attributes with the same attribute type
and value, so long as each attribute has a different language code.
Servers which support storing language codes in the DIT MUST allow any
attributes with DirectoryString to have a language code associated
with it. Servers may allow language codes 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 University
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.
Wahl, Howes [Page 6]
INTERNET-DRAFT Use of Language Codes in LDAPv3 June 1997
There is no effect of the preferredLanguage control in storing
attributes in the add operation.
4.8. 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.
There is no effect of the preferredLanguage control in performing
this operation.
4.9. Diagnostic Messages
If the server supports returning diagnostic messages in more than one
language, then if the preferredLanguage control has been set, it may
use the preferredLanguage to choose an appropriate message. If the
preferredLanguage is not recognized, the diagnostic messages MUST be
returned in the default language.
It is strongly recommended that in the default language for
diagnostic messages, only printable ASCII characters be used, as not
all clients will be able to display the full range of Unicode.
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. Bibliography
[1] M.Wahl, T. Howes, S. Kille, "Lightweight Directory Access Protocol
(Version 3)", INTERNET DRAFT
<draft-ietf-asid-ldapv3-protocol-05.txt>, June 1997.
[2] M. Wahl, A. Coulbeck, T. Howes, S. Kille, "Lightweight X.500
Directory Access Protocol Attribute Syntax Definitions",
<draft-ietf-asid-ldapv3-attributes-05.txt>, June 1997.
[3] H. Alvestrand, "Tags for the Identification of Languages",
RFC 1766, March 1995.
Wahl, Howes [Page 7]
INTERNET-DRAFT Use of Language Codes in LDAPv3 June 1997
7. Authors Addresses
Mark Wahl
Critical Angle Inc.
4815 W Braker Lane #502-385
Austin, TX 78759
USA
EMail: M.Wahl@critical-angle.com
Tim Howes
Netscape Communications Corp.
501 E. Middlefield Rd
Mountain View, CA 94043
USA
Phone: +1 415 937-3419
EMail: howes@netscape.com
<draft-ietf-asid-ldapv3-lang-02.txt> Expires: November, 1997
Wahl, Howes [Page 8]