Internet Engineering Task Force (IETF) P. Saint-Andre
Request for Comments: 6963 Cisco Systems, Inc.
BCP: 183 May 2013
Category: Best Current Practice
A Uniform Resource Name (URN) Namespace for Examples
This document defines a Uniform Resource Name (URN) namespace
identifier enabling the generation of URNs that are appropriate for
use in documentation and in URN-related testing and experimentation.
Status of This Memo
This memo documents an Internet Best Current Practice.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
BCPs is available in Section 2 of RFC 5741.
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Table of Contents
1. Introduction ....................................................2
2. Terminology .....................................................2
3. Completed Namespace Definition Template .........................3
4. Namespace Considerations ........................................4
5. Community Considerations ........................................5
6. Security Considerations .........................................5
7. IANA Considerations .............................................5
8. References ......................................................6
Appendix A. Acknowledgements .......................................7
The Uniform Resource Name (URN) technology [RFC2141] provides a way
to generate persistent, location-independent resource identifiers.
The primary "scope" of a URN is provided by its namespace identifier
(NID). As specified in [RFC3406], there are three kinds of NIDs:
formal, informal, and experimental. Most of the NIDs registered to
date are formal. As far as is known, the few informal namespaces
have not been widely used, and the experimental namespaces are by
The experimental namespaces take the form "X-NID" (where "NID" is the
desired namespace identifier). Because the "X-" convention has been
deprecated in general [RFC6648], it seems sensible to achieve the
same objective in a different way. Therefore, this document
registers a formal namespace identifier of "example", similar to
"example.com" and other domain names [RFC2606]. Under the "example"
NID, specification authors and code developers can mint URNs for use
in documentation and in URN-related testing and experimentation by
assigning their own unique Namespace Specific Strings without fear of
conflicts with current or future actual URNs. Such URNs are intended
for use as examples in documentation, testing of code for URN and URI
processing, URN-related experimentation, invalid URNs, and other
similar uses. They are not intended for testing non-URI code or for
building higher-level applications for use over the Internet or
private networks (e.g., as XML namespace names), since it is
relatively easy to mint URIs whose authority component is a domain
name controlled by the person or organization that wishes to engage
in such testing and experimentation.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
3. Completed Namespace Definition Template
3.1. Namespace ID
The Namespace ID "example" has been assigned.
3.2. Registration Information
3.3. Declared Registrant of the Namespace
Registering organization: IETF
Designated contact: IESG, firstname.lastname@example.org
3.4. Declaration of Syntactic Structure
URNs that use the "example" NID shall have the following structure:
The Namespace Specific String (NSS) is a mandatory string of ASCII
characters [RFC20] that conforms to the URN syntax requirements
[RFC2141] and provides a name that is useful within the relevant
documentation example, test suite, or other application.
3.5. Relevant Ancillary Documentation
See [RFC6648] for information about deprecation of the "X-"
convention in protocol parameters and identifiers.
3.6. Identifier Uniqueness Considerations
Those who mint example URNs ought to strive for uniqueness in the
Namespace Specific String portion of the URN. However, such
uniqueness cannot be guaranteed through the assignment process.
Therefore, it is NOT RECOMMENDED for implementers to use example URNs
for any purposes other than documentation, private testing, and truly
3.7. Identifier Persistence Considerations
Once minted, an example URN is immutable. However, it is simply a
string; and there is no guarantee that the documentation, test suite,
or other application using the URN is immutable.
3.8. Process of Identifier Assignment
Assignment is completely open, since anyone can mint example URNs for
use in documentation, private testing, and other experimental
3.9. Process for Identifier Resolution
Example URNs are not intended to be resolved, and the namespace will
probably never be registered with a Resolution Discovery System
(except to simply inform requesters that such URNs are merely
3.10. Rules for Lexical Equivalence
No special considerations; the rules for lexical equivalence
specified in [RFC2141] apply.
3.11. Conformance with URN Syntax
No special considerations
3.12. Validation Mechanism
The scope of an example URN is limited to the documentation in which
it is found, the test in which it is used, the experiment in which it
appears, etc. Example URNs have no meaning outside such strictly
4. Namespace Considerations
No existing formal namespace enables entities to generate URNs that
are appropriate for use as examples in documentation and in
URN-related testing and experimentation. It could be argued that no
such formal namespace is needed, given that experimental namespaces
can be minted at will. However, experimental namespaces run afoul of
the trend away from using the "X-" convention in the names of
protocol parameters and identifiers [RFC6648]. Additionally, in
practice, specification authors often mint examples using fake NIDs
that go unregistered because they are never intended to be used. To
minimize the possibility of confusion, use of this dedicated example
namespace is recommended for generating example URNs.
5. Community Considerations
The "example" NID is intended to provide a clean, easily recognizable
space for minting examples to be used in documentation and in
URN-related testing and experimentation. The NSS is best as a unique
string, generated by the person, organization, or other entity that
creates the documentation, test suite, or other application. There
is no issuing authority for example URNs, and it is not intended that
they can be resolved in any meaningful way.
The "example" NID does not obviate the need to coordinate with
issuing authorities for existing namespaces (e.g., minting
"urn:example:xmpp:foo" instead of requesting issuance of
"urn:xmpp:foo"), to register new namespace identifiers if existing
namespaces do not match one's desired functionality (e.g., minting
of registering the "sha-1" NID), or to respect the basic spirit of
URN NID assignment (e.g., setting up shadow NIDs such as
"urn:example:MyCompany:*" instead of using, say, HTTP URIs).
6. Security Considerations
This document introduces no additional security considerations beyond
those associated with the use and resolution of URNs in general.
7. IANA Considerations
This document defines a URN NID registration of "example", which IANA
has added to the "Formal URN Namespaces" registry. The completed
registration template can be found in Section 3.
8.1. Normative References
[RFC20] Cerf, V., "ASCII format for network interchange", RFC 20,
[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.
[RFC3406] Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom,
"Uniform Resource Names (URN) Namespace Definition
Mechanisms", BCP 66, RFC 3406, October 2002.
8.2. Informative References
[RFC2606] Eastlake, D. and A. Panitz, "Reserved Top Level DNS
Names", BCP 32, RFC 2606, June 1999.
[RFC6648] Saint-Andre, P., Crocker, D., and M. Nottingham,
"Deprecating the "X-" Prefix and Similar Constructs in
Application Protocols", BCP 178, RFC 6648, June 2012.
Appendix A. Acknowledgements
Thanks to Martin Duerst, Barry Leiba, and Jim Schaad for their
feedback; to Christer Holmberg for his Gen-ART review; and to Benoit
Claise, Adrian Farrel, and Stephen Farrell for their helpful input
during IESG review. Julian Reschke inspired the work on this
document, provided valuable suggestions, and shepherded the document.
Cisco Systems, Inc.
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