Abstract
This Architectural Specification provides authors of specifications,
software developers, and content developers with a common reference for
the use of resource identifiers building on the Universal Character Set,
defined jointly by the Unicode Standard and
ISO/IEC 10646.
For topics such as
use of the terms 'character', 'encoding' and 'string', a reference processing model, choice and identification of character encodings, character escaping, and string indexing, see Character Model for the World Wide Web 1.0: Fundamentals [CharMod]. For normalization and string identity matching, see Character Model for the World Wide Web 1.0: Normalization [CharNorm].
Status of this Document
This section describes the status of this document at the time
of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.
This document is a Candidate Recommendation of the W3C. This document has been produced by the W3C
Internationalization Working Group (I18N WG) (Members only), with the help of the Internationalization Interest Group, as part of the W3C
Internationalization Activity.
Publication as a Candidate Recommendation does not imply endorsement by the W3C
Membership. This is a draft document and may be updated, replaced or obsoleted
by other documents at any time. It is inappropriate to cite this document as
other than work in progress.
Section 3 of this document was formerly Section
7 of the Character
Model for the World Wide Web 1.0: Fundamentals Last Call Working Draft
published 25 February 2004. A more detailed change log is given in Appendix C, Changes.
The I18N WG invites comments on this specification. Comments
should be submitted by email to www-i18n-comments@w3.org
(public
archive). Please send one email per comment where possible, otherwise
number comments clearly.
The WG is soliciting implementation reports on this specification and related
technology. The WG plans to submit this specification for consideration as a
W3C Proposed Recommendation as soon as the following conditions are met:
1) The document Internationalized Resource Identifiers
(IRIs) is published as an RFC in IETF Proposed Standard status.
2) There is a test suite that tests the use of IRIs along at least the
following axes:
a) use of IRIs in several document formats;
b) use of IRIs in several locations in the same document format;
c) use of non-ASCII characters in different parts of an IRI
(e.g. domain name part, path part);
d) use of IRIs in documents with various widely used character
encodings and with characters from various scripts;
e) use of document-specific escapes in IRIs;
f) use of IRIs with various URI schemes;
g) setup of various servers for IRIs;
h) the translation of IRIs into URIs.
3) For each of the above mentioned axes, there are at least
two implementations passing the applicable tests.
4) The WG has responded formally to all issues raised against this document.
The WG is expecting that this will take at least until 15 January 2005,
but possibly longer.
Patent disclosures relevant to this specification may be found on the Working Group's patent disclosure page. This document has been produced under the 24 January 2002 CPP as amended by the W3C Patent Policy Transition Procedure. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) with respect to this specification should disclose the information in accordance with section 6 of the W3C Patent Policy.
1 Introduction
The goal of the Character Model for the World Wide Web is to facilitate use
of the Web by all people, regardless of their language, script, writing system,
and cultural conventions, in accordance with the W3C goal of universal access.
One basic prerequisite to achieve this goal is to be able to transmit and
process the characters used around the world in a well-defined and well-
understood way.
The main target audience of this specification is W3C specification
developers. This specification and parts of it can be referenced from other W3C
specifications. It defines conformance criteria for W3C specifications as well
as other specifications.
The character model described in this specification provides authors of
specifications, software developers, and content developers with a common
reference for consistent, interoperable text manipulation on the World Wide Web.
Working together, these three groups can build a more international Web.
The topic addressed in this part of the Character Model for the World Wide Web
is resource identifiers.
The topic addressed in this part of the Character Model for the World Wide Web is the character encoding of resource identifiers.
A resource identifier is a compact string of characters for identifying an abstract or physical resource.
Other parts of the Character Model address the fundamental aspects of the
model ([CharMod]) and normalization and string identity matching
([CharNorm]). For more background information, please see [CharMod].
Topics as yet not addressed or barely touched include fuzzy
matching, and language tagging. Some of these topics may be addressed in a
future versions or parts of this specification.
At the core of the model is the Universal Character Set (UCS), defined
jointly by the Unicode Standard [Unicode] and ISO/IEC 10646
[ISO/IEC 10646]. In this document, Unicode is used as a
synonym for the Universal Character Set. The model will allow Web documents
authored in the world's scripts (and on different platforms) to be exchanged,
read, and searched by Web users around the world.
2 Conformance
This section explains the conditions that specifications, software, and Web content have to fulfill to be able to claim conformance to this specification.
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 [RFC 2119].
NOTE: RFC 2119 makes it clear that requirements that use
SHOULD are not optional and must be complied with unless
there are specific reasons not to: "This word, or the adjective
"RECOMMENDED", mean that there may exist valid reasons in particular
circumstances to ignore a particular item, but the full implications must be
understood and carefully weighed before choosing a different
course."
This specification defines conformance criteria
for specifications. All
conformance criteria are
preceded by '[S]' where 'S' stands for specifications.
A specification conforms to this document if it:
does not violate any conformance criteria preceded by [S],
documents the reason for any deviation from criteria where the imperative is SHOULD, SHOULD NOT, or RECOMMENDED,
where applicable, requires implementations conforming to the specification to conform to this document,
where applicable, requires content conforming to the specification to conform to this document.
NOTE: Requirements placed on specifications might indirectly cause requirements to be placed on implementations or content that claim to conform to those specifications. Likewise, requirements placed on content may affect implementations designed to produce such content, and so on.
Where this specification places requirements on processing, it is to be understood as a way to
specify the desired external behavior. Implementations can
use other means of achieving the same results, as
long as observable behavior is not affected.
3 Character Encoding in Resource Identifiers
According to the definition in RFC 2396 [RFC 2396], URI
references are restricted to a subset of US-ASCII, with an escaping mechanism
to encode arbitrary byte values, using the %HH convention. However, the %HH
convention by itself is of limited use because there is no definitive mapping
from characters to bytes. Also, non-ASCII characters cannot be used directly.
Internationalized Resource Identifiers (IRIs)
[I-D IRI] solves both problems with an uniform approach that
conforms to the Reference Processing
Model.
C058
[S]
Specifications that define
protocol or format elements (e.g. HTTP headers, XML attributes, etc.) which are
to be interpreted as URI references (or specific subsets of URI references,
such as absolute URI references, URIs, etc.) SHOULD use
Internationalized Resource Identifiers (IRIs)
[I-D IRI] (or an appropriate subset thereof).
C059
[S]
Specifications MUST
define when the conversion from IRI references to URI references (or subsets
thereof) takes place, in accordance with Internationalized Resource
Identifiers (IRIs)
[I-D IRI].
NOTE: Document formats should allow IRIs to be used; handlers for protocols
that do not currently support IRIs can convert the IRI to a URI when
the IRI is dereferenced.
C060
[S]
Specifications that define
new syntax for URIs, such as a new URI scheme or a new kind of fragment
identifier, MUST specify that characters outside the
US-ASCII repertoire are encoded using UTF-8 and %HH-escaping.
This is in accordance
with Guidelines for new URL Schemes
[RFC 2718], Section 2.2.5.
C061
[S]
Specifications that define new syntax for URIs SHOULD also define the
normalization requirements for the syntax they introduce.