Network Working Group S. Leonard
Internet-Draft Penango, Inc.
Intended status: Standards Track September 24, 2015
Expires: March 27, 2016
URN Namespaces for XML Namespaces and RDF IRIs
draft-seantek-xmlns-rdf-urns-01
Abstract
XML segregates elements into namespaces, which can be used to mix
tags with different semantics in a composite XML document. XML
namespaces are identified by URIs (XML 1.0) or IRIs (XML 1.1).
Similarly, RDF contains "nodes" that are identified by "URI
references" (RDF 1.0) or "IRIs" (RDF 1.1). This document defines
URNs specifically for XML namespaces and RDF nodes.
Status of This Memo
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This Internet-Draft will expire on March 27, 2016.
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
1. Introduction
XML segregates elements into namespaces, which can be used to mix
tags with different semantics in a composite XML document. XML
namespaces are identified by URIs [XML1.0] or IRIs [XML1.1].
Similarly, RDF identifies nodes by "URI reference" [RDF1.0] or "IRI"
[RDF1.1]. This document defines URN namespace identifiers (NIDs)
specifically for identifying XML namespaces and RDF nodes.
Experience suggests that several URN namespace registrations have
been proposed over the years, where the primary (yet only
occasionally stated) purpose is to create concise, targeted resource
identifiers for XML or RDF use. An designer now has the option of
choosing a concise, mnemonic identifier without the cost of
maintaining and relying upon a long-lived network location (such as
an HTTP URL), and without the hassle of registering a URN namespace
identifier via IETF Consensus. One exemplary advantage of using an
xmlns URN over an HTTP URL is that even if the organization hosting
the original XML schema ceases to exist, the URI will remain
functional without needing to commandeer back an embedded domain
name.
A name in the urn:xmlns namespace uniquely and persistently
identifies an abstract XML namespace resource. The abstract resource
does not have any particular concrete representation (such as a type
of content identified by Internet media type), although concrete
representations (referenced by URIs) may be associated with it as
discussed in Section 4. Abstract parts of the abstract resource can
be identified with fragment identifiers.
A name in the urn:rdf namespace uniquely and persistently identifies
an abstract RDF node resource ("URI reference" per [RDF1.0], or "IRI"
per [RDF1.1]). The abstract resource does not have any particular
concrete representation (such as a type of content identified by
Internet media type), although concrete representations (referenced
by URIs) may be associated with it. Abstract parts of the abstract
resource can be identified with fragment identifiers.
Two distinct namespaces are valuable because each namespace
represents a different abstract resource type, which can have type-
specific concrete representations. For example,
"urn:xmlns:foobar2015" could represent some foobar2015 XML namespace,
with associated XML schema definitions. In contrast,
"urn:rdf:foobar2015" could represent some RDF node (or some RDF node
prefix), with associated description resources.
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1.1. Definitions
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.
The term "divider" means a punctuation character such as colon ":"
that serves to divide a name into parts.
The term "part" means the characters between divisions (dividers or
the ends of the name).
While a name "divided" into "parts" can be seen as forming a tree or
hierarchy, names in this specification are not hierarchical in the
[RFC3986] sense, and have no hierarchical semantic content. Names
SHOULD be treated as opaque identifiers that are only compared for
equality.
The term "initial prefix" means the first part of a name.
The term "DIGIT" is from the ABNF production in [RFC5234], i.e., the
US-ASCII characters 0 through 9.
2. Registration Template for xmlns NID
Namespace ID:
xmlns
Registration Information:
Version: 1
Date: 2015-09-24
Declared registrant of the namespace:
IETF
Declaration of syntactic structures:
An xmlns name is any
valid XML name corresponding to "Name" in Section 2.3
of [XML1.0] (production 5), with the following restrictions:
1. The name MUST be at least four characters.
2. Colons MAY be used as intra-name dividers.
3. Colons MUST NOT appear at the beginning or end of the name.
4. Consecutive colons MUST NOT appear.
and the following relaxation:
5. The first part of the name preceding the first colon MAY
be comprised of DIGITs (which are intended to correspond
to registered IANA Private Enterprise Numbers);
further discussion is in
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"Process of identifier assignment".
The ABNF of a name is:
urn-xmlns-name = [DIGIT+ ":"] NoColonNameStartChar
*([":"] NoColonNameChar)
Where the productions NoColonNameStartChar and NoColonNameChar
are respectively taken from NameStartChar (production 4)
and NameChar (production 4a) in [XML1.0], with ":" omitted.
Although ABNF is formally US-ASCII only, the domain of
this production includes the whole Unicode range.
The name is used as the basis of the
Namespace Specific String (NSS) as follows.
When the NSS is encoded in a URN in a URI protocol slot,
Unicode code points beyond U+007F
are encoded as percent-encoded UTF-8. Conveniently,
all XML name characters in the US-ASCII range are in the
[RFC3986] unreserved set.
When the NSS is encoded in a URN in a IRI protocol slot,
Unicode code points beyond U+007F in the unreserved set
are encoded as-is; they MUST NOT be percent-encoded.
Relevant ancillary documentation:
[XML1.0], [XML1.1].
Identifier uniqueness considerations:
The meaning of an identifier is registered in the registry,
and thus is unique.
Identifier persistence considerations:
Once an identifier is registered, its meaning cannot be changed.
Process of identifier assignment:
Identifiers are registered with IANA on a First-Come, First-Served
basis. One-character initial prefixes are reserved for further
use. Two- and three-character initial prefixes are intended to
correlate with language tags and regional codes; however, they
have no such semantic content when used in an xmlns name. Whole
number initial prefixes are intended to represent IANA
Private Enterprise Numbers.
Registrants are free to register names with reserved two-character
and three-character initial prefixes, such as "au:flag" or
"en:us:ca:lax". Registrants are also free to register names with
whole number prefixes, such as "20:10-250": these names have a
particular registration process since they implicitly relate
relate to IANA Private Enterprise Numbers.
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The IANA Considerations section fully defines the
registration processes.
Process for identifier resolution:
The registration for a particular identifier MAY include
any number of URIs that a URN resolver MAY use to resolve
the URN to return specific resources. The registered
URIs are not equivalent to the registered URN, so an XML document
that refers to that particular namespace MUST use the registered
URN as the XML namespace URI. IANA will maintain the resolution
database--see Section 4.
A URN resolver SHALL pass any [RFC3986] fragment component in the
urn: URI or IRI through to the resolved URI if the registered URI
does not have a fragment component. See [URNBIS].
If the registered URI has a fragment component, a URN resolver
SHALL NOT pass any [RFC3986] fragment component in the urn: URI
or IRI; the fragment component SHALL be ignored.
Rules for Lexical Equivalence:
The NSS is compared case sensitively.
If a URI and a IRI are compared against each other, the
UTF-8 percent-encoded octets in the URI representing code points
in the unreserved set beyond U+007F SHALL be treated
as the Unicode code points
in the IRI. An IRI that contains UTF-8 percent-encoded octets
in the unreserved set beyond U+007F is not supposed to exist;
it is a protocol error.
Fragments (delimited by the # character) are not considered
part of the name, the NSS, or the URN, so a fragment would not
affect lexical equivalence. Nevertheless, a urn: URI or IRI
might be produced with a fragment component.
Conformance with URN Syntax:
The URN of this namespace conforms to new URN Syntax
[URNBIS], old URN syntax [RFC2141], and Uniform Resource Identifier
(URI): Generic Syntax [RFC3986].
Validation mechanism:
An XMLNS URN may be validated by looking it up in the IANA Registry.
Scope:
Global.
3. Registration Template for rdf NID
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Namespace ID:
rdf
Registration Information:
Version: 1
Date: 2015-09-24
[[TODO: paste xmlns content and make rdf substitutions.]]
Scope:
Global.
4. IANA Considerations
This document requests the assignment of formal URN namespace IDs
"xmlns" and "rdf".
This document requests the creation of an IANA registry called
"urn:xmlns Names", and an IANA registry called "urn:rdf Names". The
registries are First-Come, First-Served [RFC5226]. Each registration
shall contain:
a. the name conforming to this document
1) in Unicode characters and
2) with characters beyond U+007F percent-encoded in UTF-8,
b. an optional description,
c. optional [RFC3986] conforming URIs that are not URNs that are to
be used for URN resolution, and
d. contact information for the registrant.
After submitting a new registration, the registration SHALL be
effective and entered into the registry after 120 hours (5 days).
Registrants or their successors may update their entries from time to
time. After submitting an updated registration, the registration
SHALL be effective and entered into the registry after 48 hours (2
days). During the waiting period, a registrant MAY withdraw the
proposed registration for any reason.
The registration template SHALL be encoded in UTF-8.
If a registrant attempts to register a name that is confusingly
similar to other registered names (such as only differing by case, or
differing by code points but generating the same or confusingly
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similar visual representations), the registrants of the prior names
are to receive a warning notification of the registration. IANA
SHOULD implement a modern algorithm to detect such confusingly
similar names.
If a registrant attempts to register a name that contains a whole
number initial prefix, the number MUST correspond to an existing IANA
Private Enterprise Number. The registrant of the corresponding IANA
Private Enterprise Number is to receive a notification of the
impending registration. The PEN registrant MAY veto the impending
registration during this time. Otherwise, the registration will
succeed.
IANA is to maintain these registries at designated URIs on its
website, currently www.iana.org. Regardless of other formatting,
IANA will designate URIs of the form: {pre}/{name}, where {pre} is
IANA's chosen name registry prefix over HTTP or HTTPS, and {name} is
the name (with UTF-8 percent-encoding). The response to an HTTP GET
request at one of these URIs SHALL be a text/plain document with
UTF-8 encoding ("charset=UTF-8") formatted as follows:
urn:{xmlns or rdf}:{name}
Description: {description}
Contact Information: {contact information}
{URI 0}
{URI 1}
{...}
The Description and Contact Information fields MAY span multiple
lines by ending the line and including one space (U+0020) on the
subsequent line. Semantically, the line-ending and space mean "end
of line" only. URN resolvers MAY use this database (whether IANA's
customary form, or the form specified by this section) when resolving
URNs to URIs to access particular resources.
The purpose of these registered URIs is to assist protocol designers,
systems analysts, and software engineers with understanding the
nature of the XML namespace or RDF node, rather than for general
consumption. For example, one registered URI could forward to a
text/html resource that is a standards document describing a protocol
that uses the URN. [[NB: compare with xml.resource.org for I-Ds.]]
Consequently, the traffic burden imposed on IANA is expected to be
negligible.
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5. Security Considerations
XML processors use XML namespaces to validate XML content. This
document is not expected to introduce any additional security
considerations beyond those inherent in XML processing.
RDF processors use RDF URI references (RDF 1.0) or IRIs (RDF 1.1) to
identify nodes (subjects, predicates, and objects). This document is
not expected to introduce any additional security considerations
beyond those inherent in RDF processing.
6. References
6.1. Normative References
[RDF1.0] Klyne, G. and J. Carroll, "Resource Description Framework
(RDF): Concepts and Abstract Syntax", World Wide Web
Consortium Recommendation REC-rdf-concepts-20040210,
February 2004,
<http://www.w3.org/TR/2004/REC-rdf-concepts-20040210>.
[RDF1.1] Cyganiak, R., Wood, D., and M. Lanthaler, "RDF 1.1
Concepts and Abstract Syntax", World Wide Web Consortium
Recommendation REC-rdf11-concepts-20140225, February 2014,
<http://www.w3.org/TR/2014/REC-rdf11-concepts-20140225/>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC
3986, January 2005.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[URNBIS] Saint-Andre, P. and J. Klensin, "Uniform Resource Names
(URNs)", draft-ietf-urnbis-rfc2141bis-urn-13 (work in
progress), September 2015.
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[XML1.0] Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
Edition)", World Wide Web Consortium Recommendation REC-
xml-20081126, November 2008,
<http://www.w3.org/TR/2008/REC-xml-20081126>.
[XML1.1] Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E.,
Yergeau, F., and J. Cowan, "Extensible Markup Language
(XML) 1.1 (Second Edition)", World Wide Web Consortium
Recommendation REC-xml11-20060816, August 2006,
<http://www.w3.org/TR/2006/REC-xml11-20060816>.
6.2. Informative References
[RFC2276] Sollins, K., "Architectural Principles of Uniform Resource
Name Resolution", RFC 2276, January 1998.
Author's Address
Sean Leonard
Penango, Inc.
5900 Wilshire Boulevard
21st Floor
Los Angeles, CA 90036
USA
Email: dev+ietf@seantek.com
URI: http://www.penango.com/
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