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Versions: (draft-saintandre-urnbis-2141bis) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 RFC 8141

URNBIS                                                    P. Saint-Andre
Internet-Draft                                                      &yet
Obsoletes: 2141, 3406 (if approved)                           J. Klensin
Intended status: Standards Track
Expires: August 10, 2015                                February 6, 2015


                     Uniform Resource Names (URNs)
                  draft-ietf-urnbis-rfc2141bis-urn-09

Abstract

   A Uniform Resource Name (URN) is a Uniform Resource Identifier (URI)
   that is assigned under the "urn" scheme and a particular URN
   namespace, typically with the intent that the URN will be a
   persistent, location-independent resource identifier or abstract
   designator.  With regard to URN syntax, this document defines the
   canonical syntax for URNs (in a way that is consistent with URI
   syntax), specifies methods for determining URN equivalence, and
   discusses URI conformance.  With regard to URN namespaces, this
   document specifies a method for defining a URN namespace and
   associating it with a namespace identifier, and describes procedures
   for registering namespace identifiers with the Internet Assigned
   Numbers Authority (IANA).  This document obsoletes both RFC 2141 and
   RFC 3406.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 10, 2015.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 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
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   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.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  URN Syntax  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Namespace Identifier Syntax . . . . . . . . . . . . . . .   5
     3.2.  Namespace Specific String Syntax  . . . . . . . . . . . .   5
     3.3.  p-component, q-component, and f-component . . . . . . . .   6
   4.  Equivalence of URNs . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Procedure . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.2.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   8
   5.  URI Conformance . . . . . . . . . . . . . . . . . . . . . . .   9
   6.  URN Namespaces  . . . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  Formal Namespaces . . . . . . . . . . . . . . . . . . . .  12
     6.2.  Informal Namespaces . . . . . . . . . . . . . . . . . . .  13
   7.  Defining a URN Namespace  . . . . . . . . . . . . . . . . . .  13
     7.1.  Purpose . . . . . . . . . . . . . . . . . . . . . . . . .  14
     7.2.  Syntax  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     7.3.  Assignment  . . . . . . . . . . . . . . . . . . . . . . .  15
     7.4.  Security and Privacy  . . . . . . . . . . . . . . . . . .  16
     7.5.  Resolution  . . . . . . . . . . . . . . . . . . . . . . .  16
   8.  Registering a URN Namespace . . . . . . . . . . . . . . . . .  17
     8.1.  Formal Namespaces . . . . . . . . . . . . . . . . . . . .  17
     8.2.  Informal Namespaces . . . . . . . . . . . . . . . . . . .  17
   9.  Guidelines for Designated Experts . . . . . . . . . . . . . .  18
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18



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     10.1.  URI Scheme . . . . . . . . . . . . . . . . . . . . . . .  18
     10.2.  Registration of URN Namespaces . . . . . . . . . . . . .  19
   11. Security and Privacy Considerations . . . . . . . . . . . . .  19
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     12.2.  Informative References . . . . . . . . . . . . . . . . .  20
   Appendix A.  Registration Template  . . . . . . . . . . . . . . .  22
     A.1.  Namespace ID  . . . . . . . . . . . . . . . . . . . . . .  22
     A.2.  Version . . . . . . . . . . . . . . . . . . . . . . . . .  22
     A.3.  Date  . . . . . . . . . . . . . . . . . . . . . . . . . .  22
     A.4.  Registrant  . . . . . . . . . . . . . . . . . . . . . . .  22
     A.5.  Purpose . . . . . . . . . . . . . . . . . . . . . . . . .  22
     A.6.  Syntax  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     A.7.  Assignment  . . . . . . . . . . . . . . . . . . . . . . .  22
     A.8.  Resolution  . . . . . . . . . . . . . . . . . . . . . . .  22
     A.9.  Documentation . . . . . . . . . . . . . . . . . . . . . .  23
     A.10. Revision Information  . . . . . . . . . . . . . . . . . .  23
   Appendix B.  Changes from RFC 2141  . . . . . . . . . . . . . . .  23
   Appendix C.  Changes from RFC 3406  . . . . . . . . . . . . . . .  23
   Appendix D.  Contributors . . . . . . . . . . . . . . . . . . . .  23
   Appendix E.  Acknowledgements . . . . . . . . . . . . . . . . . .  24
   Appendix F.  Change log for versions of draft-ietf-urnbis-
                rfc2141bis-urn . . . . . . . . . . . . . . . . . . .  24
     F.1.  Changes from -08 to -09 . . . . . . . . . . . . . . . . .  24
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  25

1.  Introduction

   A Uniform Resource Name (URN) is a Uniform Resource Identifier (URI)
   [RFC3986] that is assigned under the "urn" scheme and a particular
   namespace, typically with the intent that the URN will be a
   persistent, location-independent resource identifier or abstract
   designator.

   The assignment of URNs is done by an organization (or, in some cases,
   according to an algorithm or other automated process) that has been
   formally delegated a namespace within the "urn" scheme (e.g., a URN
   in the 'example' namespace [RFC6963] might be of the form
   "urn:example:foo").

   This document rests on two key assumptions:

   1.  Assignment of a URN is a managed process.

       A string that conforms to the URN syntax is not necessarily a
       valid URN, because a URN needs to be assigned according to the
       rules of a particular namespace (in terms of syntax, semantics,
       and process).



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   2.  The space of URN namespaces is itself managed.

       A string in the namespace identifier slot of the URN syntax is
       not necessarily a valid URN namespace identifier, because in
       order to be valid a namespace needs to be defined and registered
       in accordance with the rules specified in this document.

   So that information about both URN syntax and URN namespaces is
   available in one place, this document does the following:

   1.  Defines the canonical syntax for URNs in general (in a way that
       is consistent with URI syntax), specifies methods for determining
       URN equivalence, and discusses URI conformance.

   2.  Specifies a method for defining a URN namespace and associating
       it with a namespace identifier, and describes procedures for
       registering namespace identifiers with the Internet Assigned
       Numbers Authority (IANA).

   For URN syntax and URN namespaces, this document modernizes and
   replaces the definitions from [RFC2141] and [RFC3406].  These
   modifications build on the requirements provided in [RFC1737] and
   many years of experience with URNs, in both cases attempting to make
   the smallest reasonable set of changes from the previous definitions.

   This document obsoletes both [RFC2141] and [RFC3406].

2.  Terminology

   Several important terms used in this document are defined in the URI
   specification [RFC3986].

   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].

3.  URN Syntax

   The syntax of URNs as provided in [RFC2141] was defined before the
   updated specification of URIs in [RFC3986].  To ensure consistency
   with the URI syntax as well as semantic flexibility in the use of
   URNs within particular applications (see
   [I-D.ietf-urnbis-semantics-clarif] for further discussion), this
   specification extends the syntax of URNs to explicitly allow several
   characters (and thus URI components) that were not allowed by
   [RFC2141], and also makes several smaller syntax adjustments.




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   As a result, the syntax for a URN is defined as follows using the
   Augmented Backus-Naur Form (ABNF) as specified in [RFC5234].  Rules
   not defined below (i.e., alphanum, pchar, path-absolute, query, and
   fragment) are defined in [RFC3986].

      namestring    = assigned-name
                      [ p-component ]
                      [ q-component ]
                      [ f-component ]
      assigned-name = "urn" ":" NID ":" NSS
                    ; the URI scheme ("urn") is case insensitive
      NID           = (alphanum) 0*30(ldh) (alphanum)
      ldh           = alphanum / "-"
      NSS           = 1*(pchar)
      p-component   = "/" path-absolute
      q-component   = "?" query
      f-component   = "#" fragment

   Note that "?" can be used without %-encoding inside q-components and
   f-components.

   The following sections provide additional information about these
   rules.

3.1.  Namespace Identifier Syntax

   The syntax here is slightly more restrictive than what was defined in
   [RFC2141], since it forbids the character "-" at the end of a NID.

   NIDs are case insensitive (e.g., "ISBN" and "isbn" are equivalent).

3.2.  Namespace Specific String Syntax

   Depending on the rules governing a namespace, names that are valid in
   a namespace might contain characters that are not allowed in URNs
   according to the "pchar" rule (e.g., characters outside the ASCII
   range or characters that are reserved in URIs, such as "/", "?", and
   "#").  Such a string MUST be translated into a conformant NSS before
   using it as a protocol element or otherwise passing it on to other
   applications.  Translation is done by percent-encoding each
   disallowed character using the method defined in Section 2.1 of
   [RFC3986].  Note that the "%" character is allowed only for the
   purpose of percent-encoding.

   In order to make URNs as stable and persistent as possible when
   protocols evolve and the environment around them changes, namespaces
   SHOULD NOT allow characters outside the basic Latin repertoire




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   [RFC20] unless the nature of the particular namespace makes such
   characters necessary.

   If a namespace designates one or more characters conforming to the
   "pchar" rule as having special meaning for that namespace (e.g., "@")
   and the namespace also uses that character in a literal sense, when
   used in a literal sense the character MUST be percent-encoded (e.g.,
   "%40").  For related considerations with regard to NID registration,
   see below.

3.3.  p-component, q-component, and f-component

   The p-component, q-component, and f-component are optional components
   that follow the assigned-name.  In terms of URI syntax these
   components are essentially equivalent to the URI "path-absolute",
   "query", and "fragment" constructions, respectively.  However, the
   URN p-component, q-component, and f-component need not be
   semantically equivalent to the URI path component, query component,
   and fragment component; therefore they are called by different names
   in this specification.

   Unless specifically defined for a particular namespace after
   publication of this document, use of these components is disallowed,
   thereby maintaining strict backward compatibility with namespaces
   defined in accordance with [RFC2141] and registered in accordance
   with [RFC3406].

   This specification does not define the semantics of the p-component,
   q-component, and f-component for URNs in general.  Instead,
   additional specifications might establish these matters for URN-
   related services (such as URN resolution) or for individual URN
   namespaces (e.g., to handle extended information about the resource
   identified by a URN).  For example, it is possible that the
   q-component might be used in requests to URN resolution services, or
   that the f-component might be used to distinguish the integral parts
   of resources named by URNs in particular namespaces (say, the
   chapters of a book).  However, defining such usage is the
   responsibility of specifications for URN resolution services,
   namespace registration requests and specifications for individual
   namespaces, and other appropriate documentation (such as policy
   documents governing the management of a given URN namespace).

   As general guidance that might not apply to all cases, it would be
   inappropriate for namespaces that do not intend to support resolution
   services to allow q-components.  Namespaces which deal with digital
   manifestations might be able to support f-components.





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3.3.1.  p-component

   The only formal restriction placed upon a p-component by this
   specification is that the syntax SHALL adhere to the "path-absolute"
   rule from [RFC3986].  The inner syntax of a p-component is to be
   defined by the specification for a particular namespace or URN-
   related service.  (For example, a namespace specification might
   define a character such as "~" or "@" as a delimiter inside
   p-components assigned within that namespace.)

   As described under Section 4, the p-component SHALL be taken into
   account when determining URN equivalence.

3.3.2.  q-component

   The only formal restriction placed upon a q-component by this
   specification is that the syntax SHALL adhere to the "query" rule
   from [RFC3986] (prepended by the "?" character).  The inner syntax of
   a q-component is to be defined by the specification for a particular
   namespace.  (For example, a namespace specification might define a
   character such as ";" or "=" as a delimiter inside q-components
   assigned within that namespace.)

   As described under Section 4, the q-component SHALL NOT be taken into
   account when determining URN equivalence.

3.3.3.  f-component

   The only formal restriction placed upon an f-component by this
   specification is that the syntax SHALL adhere to the "fragment" rule
   from [RFC3986] (prepended by the "#" character).  The inner syntax of
   an f-component is to be defined by the specification for a particular
   namespace.  (For example, a namespace specification might define a
   character such as "&" or "+" as a delimiter inside f-components
   assigned within that namespace.)

   As described under Section 4, the f-component SHALL NOT be taken into
   account when determining URN equivalence.

4.  Equivalence of URNs

4.1.  Procedure

   For various purposes such as caching, often it is desirable to
   determine if two URNs are "the same".  This is done by testing for
   equivalence (see Section 6.1 of [RFC3986]).





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   Note that [RFC3986] is very flexible about equality comparisons,
   putting the focus on allowing false negatives and avoiding false
   positives.  If comparisons are made in a scheme-independent way,
   i.e., as URI comparisons only, URNs that this specification considers
   equal would be rejected.  The discussion below applies when the URI
   is known to be a URN.

   Two URNs are equivalent if they are octet-by-octet equal after
   applying case normalization (as specified in Section 6.2.2.1 of
   [RFC3986]) to the following constructs:

   1.  the URI scheme "urn"

   2.  the NID

   3.  any percent-encoded characters (see Section 2.1 of the base URI
       specification [RFC3986]) in the NSS

   Percent-encoded characters MUST NOT be decoded, i.e., percent-
   encoding normalization (as specified in Section 6.2.2.2 of [RFC3986])
   MUST NOT be applied.

   If a q-component or f-component (or both) are included in a URN, they
   MUST be ignored for purposes of determining equivalence.

   URN namespaces MAY define additional rules for equivalence, such as
   case-insensitivity of the NSS (or parts thereof).  Such rules MUST
   always have the effect of eliminating some of the false negatives
   obtained by the procedure above and MUST NOT result in treating two
   URNs as not equivalent if the procedure here says they are
   equivalent.  For related considerations with regard to NID
   registration, see below.

4.2.  Examples

   The following six URN comparisons (which use the "example" NID
   defined in [RFC6963]) highlight the equivalence rules:

   1.   URN:example:a123,456

   2.   urn:example:a123,456

   3.   urn:EXAMPLE:a123,456

   4.   urn:example:a123%2C456

   5.   URN:EXAMPLE:a123%2c456




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   6.   urn:example:A123,456

   7.   urn:example:a123,456/789

   8.   urn:example:a123,456/abc

   9.   urn:example:a123,456?789

   10.  urn:example:a123,456?abc

   11.  urn:example:a123,456#789

   12.  urn:example:a123,456#abc

   URNs 1, 2, 3, 9, 10, 11, and 12 are equivalent.  URNs 4 and 5 are
   equivalent only to each other.  URNs 6, 7, and 8 are not equivalent
   to any of the others.

5.  URI Conformance

   Because a URN is, syntactically, a URI under the "urn" scheme, in
   theory a URN can be placed in any protocol slot that allows for a URI
   (e.g., an XML namespace name [XML-NAMES]).  However, this does not
   imply that, semantically, it always makes sense in practice to place
   a URN in a given URI protocol slot; in particular, because a URN
   might not specify the location of a resource or even point indirectly
   to one, it might not be appropriate to place a URN in a URI protocol
   slot that points to a resource (examples include the 'href' and 'src'
   attributes and the <base/> element in HTML, as well as the 'xml:base'
   attribute in XML [XML-BASE]).  Ultimately, specifications of where it
   is appropriate to use URNs, or URNs created within particular URN
   namespaces, are the responsibility of descriptions of individual URI
   schemes and contexts; this specification cannot possibly anticipate
   all of the relevant cases.

   Despite the fact that URNs are not hierarchical and are not
   appropriate for use as a base URI (see Section 5.1 of [RFC3986]), the
   relative resolution algorithm specified in Section 5.2 of [RFC3986]
   still applies to the "urn" URI scheme; implementers need to be aware,
   however, that running the algorithm against URNs will lead to results
   that might be unexpected or not useful.

   A resolver that conforms to the URI specification [RFC3986] will
   extract a scheme of "urn" rather than a scheme value of "urn:<nid>".
   A URN MUST be considered an opaque URI by URI resolvers and passed
   (with the "urn" scheme) to a URN resolver for resolution.  The URN
   resolver can either be an external resolver that the URI resolver
   knows of, or it can be functionality built into the URI resolver.



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   Note that this requirement MAY impose constraints on the contexts in
   which URNs are appropriately used; see the previous section.

   To minimize user confusion, a URI browser SHOULD display the complete
   URN (including the "urn" scheme and any components) to ensure that
   there is no confusion between URN namespace identifiers and URI
   scheme identifiers.  For example, a URI beginning with "urn:xmpp:"
   [RFC4854] is very different from a URI beginning with "xmpp:"
   [RFC5122].  Similarly, a potential DOI scheme [DOI-URI] is different
   from, and possibly completely unrelated to, a possible DOI URN
   namespace.

   When URNs are transported and exchanged, they MUST be represented in
   this format.  Further, all URN-aware applications MUST offer the
   option of displaying URNs in this canonical form to allow for direct
   transcription (for example by cut and paste techniques).  Such
   applications might support display of URNs in a more human-friendly
   form and might use a character set that includes characters that are
   not permitted in URN syntax as defined in this specification (e.g.,
   when displaying URNs to humans, such applications might replace
   percent-encoded strings with characters from an extended character
   repertoire such as that of [UNICODE]).

   As mentioned, the assignment of URNs is a managed process, as is the
   assignment of namespaces themselves.  Although design of the URNs to
   be assigned within a given namespace is ceded by this specification
   to the namespace owner, doing so in a managed way avoids the problems
   inherent in unmanaged generation of URIs as described in the
   recommendations regarding URI design and ownership [RFC7320].

6.  URN Namespaces

   A URN namespace is a collection of identifiers that obey three
   constraints.  Such a namespace is (1) unique, (2) assigned in a
   consistent way, and (3) assigned according to a common definition.

   1.  The "uniqueness" constraint means that an identifier within the
       namespace is never assigned to more than one resource and never
       reassigned to a different resource, even if the identifier itself
       is deprecated or becomes obsolete.

   2.  The "consistent assignment" constraint means that an identifier
       within the namespace is assigned by an organization or created in
       accordance with a process or algorithm that is always followed.

   3.  The "common definition" constraint means that there are clear
       definitions for the syntax of identifiers within the namespace
       and for the process of assigning or creating them.



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   A URN namespace is identified by a particular NID in order to ensure
   the global uniqueness of URNs and, optionally, to provide a cue
   regarding the structure of URNs assigned within a namespace.

   With regard to global uniqueness, using different NIDs for different
   collections of identifiers ensures that no two URNs will be the same
   for different resources, since each collection is required to
   uniquely assign each identifier.  However, a single resource can have
   more than one URN assigned to it for different purposes (e.g., some
   numbers might be valid identifiers in two different identifier
   systems, where the namespace identifier differentiates between the
   resulting URNs).  Subject to other constraints, such as those imposed
   by the URI syntax [RFC3986], the rules of the URN scheme are intended
   to allow preserving the normal and natural form of identifiers
   specified elsewhere and treated as URN namespaces.

   With regard to the structure of URNs assigned within a namespace, the
   development of an identifier structure (and thereby a collection of
   identifiers) depends on the requirements of the community defining
   the identifiers, how the identifiers will be assigned and used, etc.
   These issues are beyond the scope of URN syntax and the general rules
   for URN namespaces, because they are specific to the community
   defining a namespace (e.g., the bibliographic and publishing
   communities in the case of the 'ISBN' and 'ISSN' namespaces, or the
   developers of extensions to the Extensible Messaging and Presence
   Protocol in the case of the 'XMPP' namespace).

   URN namespaces inherit certain rights and responsibilities by the
   nature of URNs, e.g.:

   1.  They uphold the general principles of a well-managed URN
       namespace by providing persistent identification of resources and
       unique assignment of identifier strings.

   2.  They can be registered in global registration services.

   There are two types of URN namespace: formal and informal.  These are
   distinguished by the expected level of service, the information
   needed to define the namespace, and the procedures for registration.
   Because the majority of the namespaces registered so far have been
   formal, this document concentrates on formal namespaces.

   Note: [RFC3406] defined a third type of "experimental namespaces",
   denoted by prefixing the namespace identifier with the string "X-".
   Consistent with [RFC6648], this specification removes the
   experimental category.  Because experimental namespaces were never
   registered, removing the experimental category has no impact on the
   existing registries or future registration procedures.  Because they



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   are not registered, strings that refer to existing experimental
   namespaces are not valid URNs.  Truly experimental usages can, of
   course, employ the 'example' namespace [RFC6963].

6.1.  Formal Namespaces

   A formal namespace provides benefit to some subset of users on the
   Internet.  In particular, it would not make sense for a formal
   namespace to be used only by a community or network that is not
   connected to the Internet.  For example, it would be inappropriate
   for a NID to effectively force someone to use a proprietary network
   or service not open to the general Internet user.  The intent is
   that, while the community of those who might actively use the names
   assigned within that NID might be small, the potential use of
   identifiers within that NID is open to any user on the Internet.
   Formal NIDs might be appropriate even when some aspects are not fully
   open.  For example, a namespace might make use of a fee-based,
   privately managed, or proprietary registry for assignment of URNs in
   the namespace.  However, it might still benefit some Internet users
   if the associated services have openly-published access protocols.

   An organization that will assign URNs within a formal namespace ought
   to meet the following criteria:

   1.  Organizational stability and the ability to maintain the URN
       namespace for a long time; absent such evidence, it ought to be
       clear how the namespace can remain viable if the organization can
       no longer maintain the namespace.

   2.  Competency in name assignment.  This will improve the likelihood
       of persistence (e.g. to minimize the likelihood of conflicts).

   3.  Commitment to not reassigning existing names and to allowing old
       names to continue to be valid, even if the owners or assignees of
       those names are no longer members or customers of that
       organization.  With regard to URN resolution [RFC2276], this does
       not mean that there needs to be resolution of such names, only
       that the names will not resolve to false or stale information.

   A formal namespace establishes a particular NID, subject to the
   following constraints (above and beyond the syntax rules already
   specified):

   1.  It MUST NOT be an already-registered NID.

   2.  It MUST NOT start with "urn-" (which is reserved for informal
       namespaces).




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   3.  It MUST be more than two characters long.

   4.  It MUST NOT start with "aa-", where "aa" is any combination of
       two ASCII letters and the hyphen is followed by something other
       than another hyphen.

   5.  It MUST NOT start with the string "xn--" or any other string
       consisting of two letters followed by two hyphens.  Those strings
       are reserved for potential representation of DNS A-labels and
       similar strings in the future [RFC5890].


   All two-letter strings, and all two-letter strings followed by "-"
   and any sequence of valid NID characters, are reserved for potential
   use as country-code-based NIDs for eventual national registrations of
   URN namespaces.  The definition and scoping of rules for allocation
   of responsibility for such country-code-based namespaces is beyond
   the scope of this document.

6.2.  Informal Namespaces

   Informal namespaces are full-fledged URN namespaces, with all the
   associated rights and responsibilities.  Informal namespaces differ
   from formal namespaces in the process for assigning a NID: for an
   informal namespace, the registrant does not designate the NID;
   instead, IANA assigns a NID consisting of the string 'urn-' followed
   by one or more digits (e.g., "urn-7") where the digits consist of the
   next available number in the sequence of positive integers assigned
   to informal namespaces.  Thus the syntax of an informal namespace is:

       InformalNamespaceName = "urn-" Number
       Number                = DigitNonZero 0*Digit
       DigitNonZero          = "1"/ "2" / "3" / "4"/ "5"
                             / "6" / "7" / "8" / "9"
       Digit                 = "0" / DigitNonZero

   The only restrictions on <Number> are that it (1) consist strictly of
   ASCII digits, that it (2) not have leading zeros, and that it (3) not
   cause the NID to exceed the length limitations defined for the URN
   syntax.

7.  Defining a URN Namespace

   The definition of a formal namespace ought to pay particular
   attention to:

   1.  The purpose of the namespace.




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   2.  The syntax of URNs assigned within the namespace, including
       whether p-, q-, and/or f-components are allowed.

   3.  The process for assigning URNs within the namespace.

   4.  The security implications of assigning URNs within the namespace
       and using the assigned URNs.

   5.  Optionally, the process for resolving URNs issued within the
       namepace.

   The following sections explain these matters in greater detail.  For
   convenience, a template for defining and registering a URN namespace
   is provided under Appendix A.  This information can be especially
   helpful to entities that wish to request assignment of a URN in a
   namespace and to entities that wish to provide URN resolution for a
   namespace.

7.1.  Purpose

   The "Purpose" section of the template describes matters such as:

   1.  The kinds of resources identified by URNs assigned within the
       namespace.

   2.  Why it is preferable to use URNs rather than some other
       technology (e.g., separate URI schemes or URIs in existing
       schemes) and why no existing URN namespace is a good fit.

   3.  The kinds of software applications that can use or resolve the
       assigned URNs (e.g., by differentiating among disparate
       namespaces, identifying resources in a persistent fashion, or
       meaningfully resolving and accessing services associated with the
       namespace).

   4.  The scope of the namespace (public vs. private, global vs. local
       to a particular organization, nation, or industry).  For example,
       a namespace claiming to deal in "national identification numbers"
       ought to have a global scope and address all identity number
       structures, whereas a URN scheme for a particular national
       identification number system would need to handle only the
       structure for that nation's identity numbers.

   5.  How the intended community (and the Internet community at large)
       will benefit from using or resolving the assigned URNs.






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7.2.  Syntax

   The "Syntax" section of the template contains:

   1.  A description of the structure of URNs within the namespace, in
       conformance with the fundamental URN syntax.  The structure might
       be described in terms of a formal definition (e.g., using
       Augmented BNF for Syntax Specifications (ABNF) as specified in
       [RFC5234]), an algorithm for generating conformant URNs, or a
       regular expression for parsing the identifier into components;
       alternatively, the structure might be opaque.

   2.  Any special character encoding rules for assigned URNs (e.g.,
       which character ought to always be used for single-quotes).

   3.  If p-components, q-components, and/or f-components are allowed
       for the namespace, a discussion of how they are used.

   4.  Rules for determining equivalence between two identifiers in the
       namespace.  Such rules ought to always have the effect of
       eliminating false negatives that might otherwise result from
       comparison.  If it is appropriate and helpful, reference can be
       made to the equivalence rules defined in the URI specification
       [RFC3986].  Examples of equivalence rules include equivalence
       between uppercase and lowercase characters in the Namespace
       Specific String, between hyphenated and non-hyphenated groupings
       in the identifier string, or between single-quotes and double-
       quotes.  (Note that these are not normative statements for any
       kind of best practice related to handling of equivalences between
       characters in general; they are statements limited to one
       particular namespace only.)

   5.  Any special considerations necessary for conforming with the URN
       syntax.  This is particularly applicable in the case of existing
       naming systems that are used in the context of URNs.  For
       example, if a namespace is used in contexts other than URNs, it
       might make use of characters that are reserved in the URN syntax.
       This section ought to note any such characters, and outline
       necessary mappings to conform to URN syntax.  Normally, this will
       be handled by percent-encoding the character as specified in the
       URI specification [RFC3986].

7.3.  Assignment

   The "Assignment" section of the template describes matters such as:

   1.  Mechanisms or authorities for assigning URNs to resources.  It
       ought to make clear whether assignment is completely open (e.g.,



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       following a particular procedure such as first-come, first-served
       (FCFS)), completely closed (e.g., for a private organization), or
       limited in various ways (e.g., delegated to authorities
       recognized by a particular organization); if limited, it ought to
       explain how to become an assigner of identifiers or how to
       request assignment of identifiers from existing assignment
       authorities.

   2.  Methods for ensuring that URNs within the namespace are unique.
       For example, identifiers might be assigned sequentially or in
       accordance with some well-defined process by a single authority,
       assignment might be partitioned among delegated authorities that
       are individually responsible for respecting uniqueness rules, or
       URNs might be created independently following an algorithm that
       itself guarantees uniqueness.

7.4.  Security and Privacy

   The "Security" section of the template describes any potential issues
   related to security and privacy with regard to assignment, use, and
   resolution of identifiers within the namespace.  Examples of such
   issues include:

   o  The consequences of producing false negatives and false positives
      during comparison for equivalence (see "Issues in Identifier
      Comparison for Security Purposes" [RFC6943])

   o  Leakage of private information when identifiers are communicated
      on the public Internet

   o  The potential for directory harvesting

   o  Various issues discussed in the guidelines for security
      considerations in RFCs [RFC3552] and the privacy considerations
      for Internet protocols [RFC6973].

7.5.  Resolution

   The "Resolution" section specifies the rules for resolution of URNs
   assigned within the namespace.  If such URNs are intended to be
   resolvable, the namespace needs to be registered in a Resolution
   Discovery System (RDS, see [RFC2276]) such as DDDS.  Resolution then
   proceeds according to standard URI resolution processes, as well as
   the mechanisms of the RDS.  This section ought to list the
   requirements for becoming a recognized resolver of URNs in the
   relevant namespace (and being so listed in the RDS registry).
   Answers might include, but are not limited to:




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   1.  The namespace is not listed with an RDS; therefore this section
       is not applicable.

   2.  Resolution mirroring is completely open, with a mechanism for
       updating an appropriate RDS.

   3.  Resolution is controlled by entities to which assignment has been
       delegated.

8.  Registering a URN Namespace

8.1.  Formal Namespaces

   The registration policy for formal namespaces is Expert Review as
   defined in the "IANA Considerations" document [RFC5226] and in
   Section 9 below.  The key steps for registration of a formal
   namespace are:

   1.  Fill out the namespace registration template (see Appendix A).
       This can be done as part of an Internet-Draft or a specification
       in another series, although that is not necessary.

   2.  Send the completed template to the urn-nid@ietf.org discussion
       list for review.

   3.  If necessary to address comments received, repeat steps 1 and 2.

   4.  If the designated experts approve the request, the IANA will
       register the requested NID.

   A formal namespace registration can be revised by updating the
   registration template, following the same steps outlined above for
   new registrations.  A revised registration MUST describe differences
   from prior versions and SHOULD make special note of any relevant
   changes in the underlying technologies or namespace management
   processes.

8.2.  Informal Namespaces

   The registration policy for informal namespaces is First Come First
   Served [RFC5226].  The key steps for registration of an informal
   namespace are:

   1.  Write a completed namespace definition template (see Appendix A).

   2.  Send it to the urn-nid@ietf.org discussion list for feedback.





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   3.  Once the review period has expired, send the final template to
       IANA (via the iana@iana.org email address).

   An informal namespace registration can be revised by updating the
   registration template, following the same steps outlined above for
   new registrations.

9.  Guidelines for Designated Experts

   Experience to date with NID registration requests has shown that
   registrants sometimes do not initially understand some of the
   subtleties of URN namespaces, and that defining the namespace in the
   form of a specification enables the registrants to clearly formulate
   their "contract" with the intended user community.  Therefore,
   although the registration policy for formal namespaces is Expert
   Review and a stable specification is not strictly required, the
   designated experts for NID registration requests ought to encourage
   applicants to provide a stable specification documenting the
   namespace definition.

   Naming can be difficult and contentious; the designated experts and
   applicants are strongly encouraged to work together in a spirit of
   good faith and mutual understanding to achieve rough consensus on
   progressing registrations through the process.  They are also
   encouraged to bring additional expertise into the discussion if that
   would be helpful in adding perspective or otherwise resolving issues.

10.  IANA Considerations

10.1.  URI Scheme

   This section updates the registration of the 'urn' URI scheme in the
   Permanent URI Registry [URI-Registry] .

   [Note to RFC Editor: please replace "XXXX" with the number assigned
   to this document upon publication.]

   URI Scheme Name:  urn

   Status:  permanent

   URI Scheme Syntax:  See Section 3 of [ this document ].

   URI Scheme Semantics:  The 'urn' scheme identifies Uniform Resource
      Names, which are persistent, location-independent resource
      identifiers.

   Encoding Considerations:  See Section 3.2 of [ this document ].



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   Applications/Protocols That Use This URI Scheme Name:  Uniform
      Resource Names are used in a wide variety of applications,
      including bibliographic reference systems and as names for
      Extensible Markup Language (XML) namespaces.

   Interoperability Considerations:  See Section 5 of [ this document ].


   Security Considerations:  See Section 7.4 and Section 11 of [ this
      document ].

   Contact:  URNBIS WG [mailto:urn@ietf.org]

   Author/Change Controller:  This scheme is registered under the IETF
      tree.  As such, the IETF maintains change control.

   References  None.

10.2.  Registration of URN Namespaces

   This document outlines the processes for registering URN namespaces,
   and has implications for the IANA in terms of registries to be
   maintained.  In all cases, the IANA ought to assign the appropriate
   NID (formal or informal) once the procedures outlined in this
   document have been completed.

11.  Security and Privacy Considerations

   The definition of a URN namespace needs to account for potential
   security and privacy issues related to assignment, use, and
   resolution of identifiers within the namespace (e.g., some namespace
   resolvers might assign special meaning to certain characters in the
   Namespace Specific String); see Section 7.4 for further discussion.

   In most cases, URN namespaces provide a way to declare public
   information.  Nominally, these declarations will have a relatively
   low security profile, however there is always the danger of
   "spoofing" and providing misinformation.  Information in these
   declarations ought to be taken as advisory.

12.  References

12.1.  Normative References

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





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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 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.

   [URI-Registry]
              IANA, "Permanent URI Schemes",
              <http://www.iana.org/assignments/uri-schemes/
              uri-schemes.xhtml#uri-schemes-1>.

12.2.  Informative References

   [I-D.ietf-urnbis-semantics-clarif]
              Klensin, J., "URN Semantics Clarification", draft-ietf-
              urnbis-semantics-clarif-00 (work in progress), August
              2014.

   [DOI-URI]  Paskin, N., Neylon, E., Hammond, T., and S. Sun, "The
              "doi" URI Scheme for the Digital Object Identifier (DOI)",
              June 2003,
              <http://tools.ietf.org/id/draft-paskin-doi-uri-04.txt>.

   [RFC1737]  Sollins, K. and L. Masinter, "Functional Requirements for
              Uniform Resource Names", RFC 1737, December 1994.

   [RFC2141]  Moats, R., "URN Syntax", RFC 2141, May 1997.

   [RFC2276]  Sollins, K., "Architectural Principles of Uniform Resource
              Name Resolution", RFC 2276, January 1998.

   [RFC3406]  Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom,
              "Uniform Resource Names (URN) Namespace Definition
              Mechanisms", BCP 66, RFC 3406, October 2002.

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552, July
              2003.





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   [RFC4854]  Saint-Andre, P., "A Uniform Resource Name (URN) Namespace
              for Extensions to the Extensible Messaging and Presence
              Protocol (XMPP)", RFC 4854, April 2007.

   [RFC5122]  Saint-Andre, P., "Internationalized Resource Identifiers
              (IRIs) and Uniform Resource Identifiers (URIs) for the
              Extensible Messaging and Presence Protocol (XMPP)", RFC
              5122, February 2008.

   [RFC5890]  Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Definitions and Document Framework",
              RFC 5890, August 2010.

   [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.

   [RFC6943]  Thaler, D., "Issues in Identifier Comparison for Security
              Purposes", RFC 6943, May 2013.

   [RFC6963]  Saint-Andre, P., "A Uniform Resource Name (URN) Namespace
              for Examples", BCP 183, RFC 6963, May 2013.

   [RFC6973]  Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
              Morris, J., Hansen, M., and R. Smith, "Privacy
              Considerations for Internet Protocols", RFC 6973, July
              2013.

   [RFC7320]  Nottingham, M., "URI Design and Ownership", BCP 190, RFC
              7320, July 2014.

   [UNICODE]  The Unicode Consortium, "The Unicode Standard, Version
              6.3", 2013,
              <http://www.unicode.org/versions/Unicode6.3.0/>.

   [XML-BASE]
              Marsh, J. and R. Tobin, "XML Base (Second Edition)", World
              Wide Web Consortium Recommendation REC-xmlbase-20090128,
              January 2009,
              <http://www.w3.org/TR/2009/REC-xmlbase-20090128>.

   [XML-NAMES]
              Thompson, H., Hollander, D., Layman, A., Bray, T., and R.
              Tobin, "Namespaces in XML 1.0 (Third Edition)", World Wide
              Web Consortium Recommendation REC-xml-names-20091208,
              December 2009,
              <http://www.w3.org/TR/2009/REC-xml-names-20091208>.




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Appendix A.  Registration Template

A.1.  Namespace ID

   Requested of IANA (formal) or assigned by IANA (informal).

A.2.  Version

   The version of the registration, starting with 1 and incrementing by
   1 with each new version.

A.3.  Date

   The date when the registration is requested of IANA, using the format
   YYYY-MM-DD.

A.4.  Registrant

   The person or organization that has registered the NID, including the
   following information:

   o  The name and address of the registering organization.

   o  The name and contact information (email, phone number, and/or
      postal address) of the designated contact person.

A.5.  Purpose

   Described under Section 7.1 of this document.

A.6.  Syntax

   Described under Section 7.2 of this document.  Unless the
   registration explicitly says otherwise, use of p-, q-, and/or
   f-components is not allowed for this namespace.

A.7.  Assignment

   Described under Section 7.3 of this document.

A.8.  Resolution

   Described under Section 7.5 of this document.








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A.9.  Documentation

   A pointer to an RFC, a specification published by another standards
   development organization, or another stable document that provides
   further information about the namespace.

A.10.  Revision Information

   (Applicable only when earlier registrations have been revised.)

   Description of changes from prior version(s).

Appendix B.  Changes from RFC 2141

   This document makes the following substantive changes from [RFC2141]:

   o  Allows p-components, q-components, and f-components.

   o  Disallows "-" at the end of a NID.

   o  Allows the "~" and "&" characters in an NSS.

   o  Formally registers 'urn' as a URI scheme.

Appendix C.  Changes from RFC 3406

   This document makes the following substantive changes from [RFC3406]:

   1.  Relaxes the registration policy for formal namespaces from "IETF
       Review" to "Expert Review" as discussed in Section 8.1 and
       Section 9.

   2.  Removes the category of experimental namespaces, consistent with
       [RFC6648].

   3.  Simplifies the registration template.

   In addition, some of the text has been updated to be consistent with
   the definition of Uniform Resource Identifiers (URIs) [RFC3986] and
   the processes for registering information with the IANA [RFC5226], as
   well as more modern guidance with regard to security issues [RFC3552]
   and identifier comparison [RFC6943].

Appendix D.  Contributors

   RFC 2141, which provided the basis for the syntax portion of this
   document, was authored by Ryan Moats.




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   RFC 3406, which provided the basis for the namespace portion of this
   document, was authored by Leslie Daigle, Dirk-Willem van Gulik,
   Renato Iannella, and Patrik Faltstrom.

   Their work is gratefully acknowledged.

Appendix E.  Acknowledgements

   Many thanks to Marc Blanchet, Leslie Daigle, Martin Duerst, Juha
   Hakala, Ted Hardie, Alfred Hoenes, Paul Jones, Barry Leiba, Sean
   Leonard, Larry Masinter, Keith Moore, Mark Nottingham, Julian
   Reschke, Lars Svensson, Dale Worley, and other participants in the
   URNBIS WG for their input.  Alfred Hoenes in particular edited an
   earlier version of this document and served as co-chair of the URNBIS
   WG.

   Juha Hakala deserves special recognition for his dedication to
   successfully completing this work, as do Andrew Newton in his role as
   working group chair and Barry Leiba in his role as area director.

Appendix F.  Change log for versions of draft-ietf-urnbis-rfc2141bis-urn

   [[RFC Editor: please remove this appendix before publication.]]

F.1.  Changes from -08 to -09

   o  Altered the text in Section 5 to reflect list discussions about
      the earlier phrasing.  Also added DOI example and citation to that
      section.

   o  Clarified the naming rules for formal namespaces and their
      relationship to ISO 3166, IDNA, etc., reserved strings.

   o  Added an explicit statement about use of URNs in various protocols
      and contexts to Section 5.

   o  Clarified that experimental namespace NIDs, which were explicitly
      not registered, are not valid URNs (in Section 6.

   o  Transformed the partial production in Section 6.2 into valid ABNF.

   o  Added more text about p-/q-/f-components and recommendations about
      use.

   o  Added clarifying note about "?" within q-components and
      f-components.





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   o  Added explicit requirement that revisions of existing
      registrations document the changes and added a slot for that
      description to the template.

   o  Many small editorial changes and adjustments including adding
      additional references and cross-references for clarification.

   o  Inserted a placeholder for additional examples.

Authors' Addresses

   Peter Saint-Andre
   &yet

   Email: peter@andyet.com
   URI:   https://andyet.com/


   John C Klensin
   1770 Massachusetts Ave, Ste 322
   Cambridge, MA  02140
   USA

   Phone: +1 617 245 1457
   Email: john-ietf@jck.com


























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