A URN Namespace for Public Identifiers
RFC 3151
| Document | Type |
RFC - Informational
(August 2001; No errata)
Was draft-walsh-urn-publicid (individual)
|
|
|---|---|---|---|
| Last updated | 2013-03-02 | ||
| Stream | Legacy | ||
| Formats | plain text pdf html bibtex | ||
| Stream | Legacy state | (None) | |
| Consensus Boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | RFC 3151 (Informational) | |
| Telechat date | |||
| Responsible AD | (None) | ||
| Send notices to | (None) | ||
Network Working Group N. Walsh
Request for Comments: 3151 Sun Microsystems, Inc.
Category: Informational J. Cowan
Reuters Health Information
P. Grosso
Arbortext, Inc.
August 2001
A URN Namespace for Public Identifiers
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
This document describes a URN (Uniform Resource Name) namespace that
is designed to allow Public Identifiers to be expressed in URI
(Uniform Resource Identifiers) syntax.
1. Introduction
XML [1] external entities have two identifiers: a system identifier
and a public identifier. The system identifier is a URI, by
definition, but the public identifier is simply a string.
Historically, the system identifier of an external entity has been a
local, or system-specific identifier while the public identifier has
been a more global, persistent name.
Unfortunately, public identifiers do not fit neatly into the existing
web architecture because they are not legal URIs. Many new
specifications (XSLT, XML Schema, etc.) have the implicit or explicit
requirement that all external identifiers be URIs.
The purpose of this namespace is to allow public identifiers to be
encoded in URNs in a reliable, comparable way.
Walsh, et al. Informational [Page 1]
RFC 3151 A URN Namespace for Public Identifiers August 2001
This document describes a scheme for representing public identifiers
as URNs by introducing a public identifier namespace, "publicid".
This namespace specification is for a formal namespace.
1.1 Public Identifiers
Any string which consists only of the public identifier characters
(defined by Production 13 of Extensible Markup Language (XML) 1.0
Second Edition [1]) is a legal public identifier.
In addition to the character set restriction, public identifiers must
be normalized by changing all strings of whitespace (the characters
#x20, #x9, #xD, and #xA) to single space characters (#x20), and
removing all leading and trailing whitespace.
In keeping with this specification's goal of allowing public
identifiers to be encoded in a reliable, comparable way, this
specification mandates that public identifiers be normalized before
encoding them into URNs. Throughout this specification, we assume
that normalization has already been performed.
1.2 Formal Public Identifiers
SGML [2] defines a restricted subset of public identifier called a
"Formal Public Identifier" (FPI).
FPIs are strings composed from the same range of characters as public
identifiers, but with an explicit internal structure. The structure
of Formal Public Identifiers is normatively described in SGML [2]; we
review it here for convenience.
Most Formal Public Identifiers consist of the following fields, in
this order: an owner identifier, a public text class, a public text
description, a public text language or public text designating
sequence, and an optional public text display version.
Owner identifiers may begin with "-//" or "+//"; otherwise "//" is
used to delimit fields in the FPI (with the exception of the public
text class which is delimited from the public text description by a
space).
In other words, most FPIs look like this:
owner//class description//language//version
and most owners begin with "+//" or "-//", although they are not
required to. Here are some example FPIs:
Walsh, et al. Informational [Page 2]
RFC 3151 A URN Namespace for Public Identifiers August 2001
+//IDN python.org//DTD XML Bookmark Exchange Language 1.0//EN//XML
-//OASIS//DTD DocBook XML V4.1.2//EN
-//ArborText::prod//DTD Help Navigation Document::19970708//EN
ISO/IEC 10179:1996//DTD DSSSL Architecture//EN
ISO 8879:1986//ENTITIES Added Latin 1//EN
This document describes an algorithm for encoding public identifiers
into URNs that explicitly allows the structured nature of formal
public identifiers to be preserved. However, an algorithm for
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