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Internet Engineering Task Force (IETF)                    P. Saint-AndreRequest for Comments: 6963                           Cisco Systems, Inc.BCP: 183                                                        May 2013Category: Best Current PracticeISSN: 2070-1721A Uniform Resource Name (URN) Namespace for ExamplesAbstract   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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6963.Copyright Notice   Copyright (c) 2013 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) 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 2013Table of Contents1. Introduction ....................................................22. Terminology .....................................................23. Completed Namespace Definition Template .........................34. Namespace Considerations ........................................45. Community Considerations ........................................56. Security Considerations .........................................57. IANA Considerations .............................................58. References ......................................................6Appendix A. Acknowledgements .......................................71.  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   "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.2.  Terminology   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   [RFC2119].Saint-Andre               Best Current Practice                 [Page 2]

RFC 6963                      Example URNs                      May 20133.  Completed Namespace Definition Template3.1.  Namespace ID   The Namespace ID "example" has been assigned.3.2.  Registration Information   Version 1   Date: 2013-04-243.3.  Declared Registrant of the Namespace   Registering organization: IETF   Designated contact: IESG, iesg@ietf.org3.4.  Declaration of Syntactic Structure   URNs that use the "example" NID shall have the following structure:   urn:example:{NSS}   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 20133.8.  Process of Identifier Assignment   Assignment is completely open, since anyone can mint example URNs for   use in documentation, private testing, and other experimental   contexts.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   examples).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 considerations3.12.  Validation Mechanism   None3.13.  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 20135.  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 inSection 3.Saint-Andre               Best Current Practice                 [Page 5]

RFC 6963                      Example URNs                      May 20138.  References8.1.  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 2013Appendix 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   USA   EMail: psaintan@cisco.comSaint-Andre               Best Current Practice                 [Page 7]