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Internet Engineering Task Force (IETF) P. Saint-Andre Request for Comments: 6963 Cisco Systems, Inc. BCP: 183 May 2013 Category: Best Current Practice ISSN: 2070-1721

        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.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at

Copyright Notice

 Copyright (c) 2013 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 ( in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Saint-Andre Best Current Practice [Page 1] RFC 6963 Example URNs May 2013

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

1. Introduction

 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
 definition unregistered.
 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
 "" 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.

2. Terminology

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "OPTIONAL" in this document are to be interpreted as described in

Saint-Andre Best Current Practice [Page 2] RFC 6963 Example URNs May 2013

3. Completed Namespace Definition Template

3.1. Namespace ID

 The Namespace ID "example" has been assigned.

3.2. Registration Information

 Version 1
 Date: 2013-04-24

3.3. Declared Registrant of the Namespace

 Registering organization: IETF
 Designated contact: IESG,

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
 experimental contexts.

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.

Saint-Andre Best Current Practice [Page 3] RFC 6963 Example URNs May 2013

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


3.13. Scope

 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
 limited contexts.

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.

Saint-Andre Best Current Practice [Page 4] RFC 6963 Example URNs May 2013

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
 "urn:example:sha-1:29ead03e784b2f636a23ffff95ed12b56e2f2637" instead
 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.

Saint-Andre Best Current Practice [Page 5] RFC 6963 Example URNs May 2013

8. References

8.1. Normative References

 [RFC20]    Cerf, V., "ASCII format for network interchange", RFC 20,
            October 1969.
 [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.

Saint-Andre Best Current Practice [Page 6] RFC 6963 Example URNs May 2013

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.

Author's Address

 Peter Saint-Andre
 Cisco Systems, Inc.
 1899 Wynkoop Street, Suite 600
 Denver, CO  80202

Saint-Andre Best Current Practice [Page 7]

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