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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: December 17, 2015                                 June 15, 2015


                     Uniform Resource Names (URNs)
                  draft-ietf-urnbis-rfc2141bis-urn-12

Abstract

   A Uniform Resource Name (URN) is a Uniform Resource Identifier (URI)
   that is assigned under the "urn" scheme and a particular URN
   namespace, with the intent that the URN will be either a persistent,
   location-independent resource identifier or in some cases an abstract
   designator that is persistent but that does not identify a resource.
   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
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   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 December 17, 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
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   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
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   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  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Namespace Identifier  . . . . . . . . . . . . . . . . . .   6
     3.2.  Namespace Specific String . . . . . . . . . . . . . . . .   6
     3.3.  Optional Components . . . . . . . . . . . . . . . . . . .   7
   4.  Equivalence of URNs . . . . . . . . . . . . . . . . . . . . .   9
     4.1.  Procedure . . . . . . . . . . . . . . . . . . . . . . . .   9
     4.2.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .  10
   5.  URI Conformance . . . . . . . . . . . . . . . . . . . . . . .  11
     5.1.  Use in URI Protocol Slots . . . . . . . . . . . . . . . .  11
     5.2.  Parsing . . . . . . . . . . . . . . . . . . . . . . . . .  12
     5.3.  URNs and Relative References  . . . . . . . . . . . . . .  12
     5.4.  Transport and Display . . . . . . . . . . . . . . . . . .  13
     5.5.  URI Design and Ownership  . . . . . . . . . . . . . . . .  13
   6.  URN Namespaces  . . . . . . . . . . . . . . . . . . . . . . .  13
     6.1.  Formal Namespaces . . . . . . . . . . . . . . . . . . . .  15
     6.2.  Informal Namespaces . . . . . . . . . . . . . . . . . . .  17
   7.  Defining and Registering a URN Namespace  . . . . . . . . . .  17
     7.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .  17
     7.2.  Registration Policy and Process . . . . . . . . . . . . .  18
     7.3.  Completing the Template . . . . . . . . . . . . . . . . .  19
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
     8.1.  URI Scheme  . . . . . . . . . . . . . . . . . . . . . . .  22



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     8.2.  Registration of URN Namespaces  . . . . . . . . . . . . .  23
   9.  Security and Privacy Considerations . . . . . . . . . . . . .  23
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  23
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  23
     10.2.  Informative References . . . . . . . . . . . . . . . . .  24
   Appendix A.  Registration Template  . . . . . . . . . . . . . . .  26
     A.1.  Namespace ID  . . . . . . . . . . . . . . . . . . . . . .  26
     A.2.  Version . . . . . . . . . . . . . . . . . . . . . . . . .  26
     A.3.  Date  . . . . . . . . . . . . . . . . . . . . . . . . . .  26
     A.4.  Registrant  . . . . . . . . . . . . . . . . . . . . . . .  26
     A.5.  Purpose . . . . . . . . . . . . . . . . . . . . . . . . .  26
     A.6.  Syntax  . . . . . . . . . . . . . . . . . . . . . . . . .  26
     A.7.  Assignment  . . . . . . . . . . . . . . . . . . . . . . .  27
     A.8.  Security and Privacy  . . . . . . . . . . . . . . . . . .  27
     A.9.  Interoperability  . . . . . . . . . . . . . . . . . . . .  27
     A.10. Resolution  . . . . . . . . . . . . . . . . . . . . . . .  27
     A.11. Documentation . . . . . . . . . . . . . . . . . . . . . .  27
     A.12. Revision Information  . . . . . . . . . . . . . . . . . .  27
   Appendix B.  Changes from RFC 2141  . . . . . . . . . . . . . . .  27
   Appendix C.  Changes from RFC 3406  . . . . . . . . . . . . . . .  27
   Appendix D.  Contributors . . . . . . . . . . . . . . . . . . . .  28
   Appendix E.  Acknowledgements . . . . . . . . . . . . . . . . . .  28
   Appendix F.  Change log for versions of draft-ietf-urnbis-
                rfc2141bis-urn . . . . . . . . . . . . . . . . . . .  28
     F.1.  Changes from -08 to -09 . . . . . . . . . . . . . . . . .  28
     F.2.  Changes from -09 to -10 . . . . . . . . . . . . . . . . .  29
     F.3.  Changes from -10 to -11 . . . . . . . . . . . . . . . . .  29
     F.4.  Changes from -11 to -12 . . . . . . . . . . . . . . . . .  30
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  30

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, with the intent that the URN will be either a persistent,
   location-independent resource identifier or in some cases an abstract
   designator that is persistent but that does not identify a resource.
   A URN namespace is a collection of such identifiers, each of which is
   (1) unique, (2) assigned in a consistent and managed way, and (3)
   assigned according to a common definition.

   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:



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   1.  Assignment of a URN is a managed process.

   2.  The space of URN namespaces is itself managed.

   While other URI schemes may allow identifiers to be freely chosen and
   assigned, such is not the case for URNs.  The syntactical correctness
   of a string starting with "urn:" is not sufficient to make it a URN.
   In order for the string to be a valid URN, the namespace identifier
   must be registered in accordance with the rules defined here and the
   remaining parts of the full assigned-name portion of the URN must be
   generated in accordance with the rules for the registered namespace.

   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.
   The intent is to define URNs in a consistent manner so that, wherever
   practical, the parsing, handling, and resolution of URNs can be
   independent of the namespace within which a given URN is assigned.

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

2.  Terminology

   Several important terms used in this document, including some
   "normalization" operations that are not part of the Unicode Standard
   [UNICODE], 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].






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3.  URN Syntax

   The syntax of URNs as provided in [RFC2141] was defined before the
   updated specification of URIs in [RFC3986].  In order 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 does the following:

   o  Extends URN syntax to explicitly allow the characters '/', "?",
      and "#", which were reserved for future use by [RFC2141]; this
      change effectively also allows several components of the URI
      syntax although without tying those components to URI semantics.

   o  Defines syntax for an additional component that can be used in
      interactions with a URN resolution service.

   o  Makes several smaller syntax adjustments.

   However, this specification does not extend the URN syntax to allow
   characters outside the ASCII range [RFC20], which implies that any
   such characters need to be percent-encoded as described in
   Section 2.1 of the URI specification [RFC3986].

   The syntax for a URN is defined as follows using the Augmented
   Backus-Naur Form (ABNF) as specified in [RFC5234].  Rules not defined
   here (i.e., alphanum, pchar, path-absolute, query, and fragment) are
   defined as part of the URI syntax [RFC3986] and used here to point
   out the syntactic relationship with the terms used there.

      namestring    = assigned-name
                      [ "?" q-string ]
                      [ "??" r-string ]
                      [ "#" f-string ]
      assigned-name = "urn" ":" NID ":" NSS
      NID           = (alphanum) 0*30(ldh) (alphanum)
      ldh           = alphanum / "-"
      NSS           = pchar *(pchar / "/")
      q-string      = pchar *( pchar / "/" / "?" )
      r-string      = pchar *( pchar / "/" / "?" )
      f-string      = fragment

   Note: The character "?" can be used without percent-encoding inside
   q-components, r-components, and f-components.

   The following sections provide additional information about the
   syntactic elements of URNs.




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3.1.  Namespace Identifier

   The syntax here is slightly more restrictive than what was defined in
   [RFC2141].  This specification prohibits the character "-" at the end
   of a NID.

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

   Characters outside the ASCII range [RFC20] are not permitted in NIDs,
   and no encoding mechanism for such characters is supported.

3.2.  Namespace Specific String

   The namespace specific string (NSS) is a unique identifier that is
   assigned and managed in a consistent way and that conforms to the
   definition of the relevant namespace.  The combination of the NID
   (unique across the entire "urn" scheme) and the NSS (unique within
   the namespace) ensures that the resulting URN is a globally unique
   URI.

   This document modifies the syntax of the NSS to allow the following
   characters: "/", "~", and "&".

   In particular, allowing the "/" character effectively makes it
   possible to encapsulate hierarchical identifiers from other naming
   systems.  For instance, consider the hypothetical example of a
   hierarchical naming system in which the identifiers take the form of
   a series of numbers separated by the "/" character, such as "1/406/
   47452/2".  If the naming authority for such identifiers were to use
   URNs, it would be natural to place the existing identifiers in the
   NSS, resulting in URNs such as "urn:example:1/406/47452/2".

   Depending on the rules governing a namespace, names that are valid in
   a namespace might contain characters that are not allowed by the
   "pchar" production referenced above (e.g., characters outside the
   ASCII range or characters that are reserved in URIs, such as "?", and
   "#").  While such a string might be a valid name, it is not a valid
   URN until it has been translated into a conformant NSS.  Translation
   is done by percent-encoding each disallowed character using the
   method defined in Section 2.1 of the generic URI specification
   [RFC3986].  Note that the "%" character is allowed in the NSS 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
   [RFC20] unless the nature of the particular namespace makes such
   characters necessary.



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   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 Section 7.3.2.

3.3.  Optional Components

   The q-component, r-component, and f-component are optional components
   that follow the assigned-name portion of the URN.

   Because this specification focuses almost exclusively on URN syntax,
   it does not define the semantics of the q-component, r-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).
   Defining the details of such usage is the responsibility of
   specifications for URN resolution services, namespace registration
   requests or specifications for individual namespaces, and other
   appropriate documentation (such as policy documents governing the
   management of a given URN namespace).

   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].

3.3.1.  q-component

   Although the URN q-component has close to the same syntax as the URI
   query component, the URN q-component need not be semantically
   equivalent to the URI query component and therefore is called by a
   different name in this specification to emphasize that the
   relationship is about syntax only (see also
   [I-D.ietf-urnbis-semantics-clarif]).

   The q-component is indicated by the first question mark ("?")
   character and terminated by a double question mark ("??"), by a
   number sign ("#") character, or by the end of the URI.  The q-string
   MUST NOT begin with a question mark ("?") since a double question
   mark is reserved for use by an r-component (Section 3.3.2).  The
   characters slash ("/") and question mark ("?") may represent data
   within the q-string.  Note that characters outside the ASCII range
   [RFC20] MUST be percent-encoded using the method defined in
   Section 2.1 of the generic URI specification [RFC3986].



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

   The q-component is primarily intended to be used for passing
   information in requests to the resources identified by a URN or to
   applications that manage such resources.  Consider the hypothetical
   example of passing parameters to an application that returns metadata
   about a resource (say, Dublin Core [RFC5013] data about a published
   book).  This could perhaps be accomplished by specifying the desired
   metadata field (e.g., "description") in the q-component, resulting in
   URNs such as
   "urn:example:0-395-36341-1?operation=search&field=description".
   However, this primary purpose is not intended to forestall other
   potential uses for q-components.

3.3.2.  r-component

   The URN r-component has no syntactic equivalent in URIs.

   The r-component is indicated by a double question mark ("??") and
   terminated by a number sign ("#") character or by the end of the URI.
   The characters slash ("/") and question mark ("?") may represent data
   within the r-string.  Note that characters outside the ASCII range
   [RFC20] MUST be percent-encoded using the method defined in
   Section 2.1 of the generic URI specification [RFC3986].

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

   The r-component is primarily intended to be used for passing
   information in requests to URN resolution services (not, as with the
   q-component, to the resources identified by a URN or to applications
   that manage such resources).  Consider the hypothetical example of
   passing parameters to resolution service (say, an ISO alpha-2 country
   code [ISO3166-1] in order to scope down the preferred country in
   which to search for a physical copy of a book).  This could perhaps
   be accomplished by specifying the country code in the r-component,
   resulting in URNs such as "urn:example:0-395-36341-1??cc=uk".
   However, this primary purpose is not intended to forestall other
   potential uses for r-components.

   This document defines only the syntax of the r-component and reserves
   it for future use.  The exact semantics of the r-component and its
   use in URN resolution protocols are a matter for potential
   standardization in separate specifications.






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3.3.3.  f-component

   Although the URN f-component has the same syntax as the URI fragment
   component, the URN f-component need not be semantically equivalent to
   the URI fragment component and therefore is called by a different
   name in this specification to emphasize that the relationship is
   about syntax only (see also [I-D.ietf-urnbis-semantics-clarif]).

   The f-component is indicated by the presence of a number sign ("#")
   character and terminated by the end of the URI.  Note that characters
   outside the ASCII range [RFC20] MUST be percent-encoded using the
   method defined in Section 2.1 of the generic URI specification
   [RFC3986].

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

   The f-component is primarily intended to distinguish the integral
   parts of resources named by URNs in particular namespaces.  Consider
   the hypothetical example of obtaining resources that are part of a
   larger entity (say, the chapters of a book).  Each part could be
   specified in the f-component, resulting in URNs such as
   "urn:example:978-952-10-7060-0#chapter1".  However, this primary
   purpose is not intended to forestall other potential uses for
   f-components.

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]).

   The generic URI specification [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 URIs involved are known to be URNs.

   Two URNs are equivalent if their <assigned-name> portions 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", by conversion to lower case

   2.  the NID, by conversion to lower case



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   3.  any percent-encoded characters in the NSS (that is, all character
       triplets that match the <pct-encoding> production found in
       Section 2.1 of the base URI specification [RFC3986]), by
       conversion to upper case for the digits A-F.

   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, r-component, or f-component (or any combination
   thereof) are included in a URN, they MUST be ignored for purposes of
   determining equivalence.

   URN namespace definitions MAY include 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

   This section shows a variety of URNs (using the "example" NID defined
   in [RFC6963]) that highlight the equivalence rules.

   First, because the scheme and NID are case-insensitive, the following
   URNs are equivalent to each other:

   o  urn:example:a123,z456

   o  URN:example:a123,z456

   o  urn:EXAMPLE:a123,z456

   Second, because the q-component and f-component are not taken into
   account for purposes of testing equivalence, the following URNs are
   equivalent to the first three examples above:

   o  urn:example:a123,z456?abc

   o  urn:example:a123,z456#789

   o  urn:example:a123,z456#abc

   Third, because the "/" character (and anything that follows it) in
   the NSS is taken into account for purposes of equivalence, the




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   following URNs are not equivalent to each other or to the preceding
   URNs:

   o  urn:example:a123,z456/foo

   o  urn:example:a123,z456/bar

   o  urn:example:a123,z456/baz

   Fourth, because of percent-encoding, the following URNs are
   equivalent only to each other (although %2C is the percent-encoded
   transformation of "," from the previous examples, such sequences are
   not decoded for purposes of testing equivalence):

   o  urn:example:a123%2Cz456

   o  URN:EXAMPLE:a123%2cz456

   Fifth, because characters other than percent-encoded sequences in the
   NSS are treated in a case-sensitive manner (unless otherwise
   specified for the namespace in question), the following URNs are not
   equivalent to the first three URNs:

   o  urn:example:A123,z456

   o  urn:example:a123,Z456

   Sixth, on casual visual inspection of a URN presented in a human-
   oriented interface the following URN might appear the same as the
   first three URNs (since U+0430 CYRILLIC SMALL LETTER A can be
   confused with U+0061 LATIN SMALL LETTER A), but it is not equivalent:

   o  urn:example:%D0%B0123,z456

5.  URI Conformance

5.1.  Use in URI Protocol Slots

   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., the 'href' and 'src' attributes in HTML, the <base/> element
   in HTML, the 'xml:base' attribute in XML [XML-BASE], and the 'xmlns'
   attribute in XML for XML namespace names [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



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   to place a URN in a URI protocol slot that points to a resource
   (e.g., the aforementioned 'href' and 'src' attributes).

   Ultimately, guidelines regarding when it is appropriate to use URIs
   under the "urn" scheme (or any other scheme) are the responsibility
   of specifications for individual URI protocol slots (e.g., the
   specification for the 'xml:base' attribute in XML might recommend
   that it is inappropriate to use URNs in that protocol slot).  This
   specification cannot possibly anticipate all of the relevant cases,
   and it is not the place of this specification to require or restrict
   usage for individual protocol slots.

5.2.  Parsing

   In part because of the separation of semantics from syntax
   [I-D.ietf-urnbis-semantics-clarif], generic URI processors need to
   pay special attention to the parsing and analysis rules of RFC 3986
   and, in particular, must treat the URI as opaque unless the scheme
   and its requirements are recognized, in which case they may be in a
   position to invoke scheme-appropriate processing such as by a URN
   resolver.  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.  Note that this requirement might impose constraints on
   the contexts in which URNs are appropriately used; see Section 5.1.

5.3.  URNs and Relative References

   [RFC3986] Section 5.2 describes an algorithm for converting a URI
   reference that might be relative to a given base URI into "parsed
   components" of the target of that reference, which can then be
   recomposed per RFC 3986 Section 5.3 into a target URI.  This
   algorithm cannot be applied directly to URNs because their syntax
   does not support the necessary path components.  The notion of a URN
   as a "persistent", "permanent" identifier does not reconcile easily
   with relative referencing.  However, resources named with URNs may
   contain relative references that do not apply to the URN itself.

   Therefore a relative reference SHOULD NOT be evaluated directly with
   respect to a URN.  Instead, a relative reference SHOULD be evaluated
   indirectly with respect to one of the following:

   1.  a base URI (other than a URN) declared by the resource itself; or

   2.  a base URI (other than a URN) obtained through the URN resolution
       process; or

   3.  the URL of the resource as obtained through the URN resolution
       process



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   (Case 2 permits the resolution process to explicitly supply a base
   URI if the resource content is supplied directly by the resolution
   service rather than via an intermediate "location" URI.)

   If no such base URI exists, use of a relative reference with respect
   to a URN is an error and will yield results that might be unexpected
   or not useful.

   Resolution services SHOULD ensure that a base URI is supplied any
   time they provide resource content directly to a client.

5.4.  Transport and Display

   When URNs are transported and exchanged, they MUST be represented in
   the format defined herein.  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 Unicode [UNICODE]).

   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 URI scheme [DOI-URI] is
   different from, and possibly completely unrelated to, a possible DOI
   URN namespace.

5.5.  URI Design and Ownership

   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: each identifier is (1) unique, (2) assigned in a
   consistent way, and (3) assigned according to a common definition.




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   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.

   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 (for example,
   if a book were published in a monograph series, it could have both an
   ISBN [RFC3187] and an ISSN [RFC3044] assigned to it, resulting in two
   URNs referring to the same book).  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 when they are 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 in accordance with a
       common definition.



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   2.  Optionally, 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 general IETF conclusions about similar approaches
   [RFC6648], this specification removes the experimental category and
   syntax.  Because experimental namespaces were never registered,
   removing the experimental category has no impact on the existing
   registries or future registration procedures.  Because they 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 identifiers.

   An organization that will assign URNs within a formal namespace
   SHOULD 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).




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   3.  Commitment to not reassigning existing names and to allowing old
       names to continue to be valid (e.g., if the assignee of a name is
       no longer a member or customer of the assigning organization, if
       various information about the assignee or named entity happens to
       change, or even if the assignee or the named entity itself is no
       longer in existence; in all these cases, the name is still
       valid).

   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).

   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 NIDs based on ISO alpha-2 country codes [ISO3166-1] 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.

   Applicants and reviewers considering new NIDs should also be aware
   that they may be considered as names with semantic implications and
   hence a source of conflict.  Particular attention should be paid to
   strings that might be construed as names of, or registered under the
   authority of, countries (including ISO 3166-1 alpha-3 codes) and to
   strings that might imply association with well-known trademarks.  In
   line with traditional policies, disputes about "ownership" of
   particular strings are disagreements among the parties involved;
   neither IANA nor the IETF will become involved in such disputes
   except in response to orders from a court of competent jurisdiction.






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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 and Registering a URN Namespace

7.1.  Overview

   Because the space of URN namespaces is itself managed, the definition
   of a namespace SHOULD pay particular attention to:

   1.  The purpose of the namespace.

   2.  The syntax of URNs assigned within the namespace, including
       whether q-components, r-components, 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.  Any potential interoperability issues with URNs assigned within
       the namespace.

   6.  Optionally, the process for resolving URNs issued within the
       namespace.

   The section on completing the template (Section 7.3) explains these
   matters in greater detail.




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7.2.  Registration Policy and Process

   The basic registration policy for URN namespaces is Expert Review as
   defined in the "IANA Considerations" document [RFC5226].  For
   namespaces or their definitions that are intended to become standards
   or normative components of standards, the output of the Expert Review
   process is intended to be a report, rather than instructions to IANA
   to take action (see below).  The key steps are:

   1.  Fill out the namespace registration template (see Section 7.3 and
       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@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 and no
       standardization action is involved, the IANA will register the
       requested NID.  If standardization is anticipated, the designated
       experts will prepare a report and forward it to the appropriate
       standards approval body (the IESG in the case of the IETF) and
       IANA will register the requested NID only after receiving
       directions from that body and a copy of the expert review report.

   A 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.

   Experience to date with namespace 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 specification is not strictly required, it is
   RECOMMENDED for registrants to provide a stable specification
   documenting the namespace definition and expanding upon the issues
   described herein.

   Because naming can be difficult and contentious, namespace
   registrants and the designated experts are strongly encouraged to
   work together in a spirit of good faith and mutual understanding to
   achieve rough consensus (see [RFC7282]) on handling registration
   requests.  They are also encouraged to bring additional expertise



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   into the discussion if that would be helpful in providing perspective
   or otherwise resolving issues.

   Especially when iterations in the registration process are prolonged,
   designated experts are expected to take reasonable precautions to
   avoid race conditions on proposed NID names and, if such situations
   arise, to encourage applicants to work out any conflicts among
   themselves.

7.3.  Completing the Template

   A template for defining and registering a URN namespace is provided
   in Appendix A.  This section describes considerations for completing
   the template.

7.3.1.  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"
       might be expected 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.

   6.  If the namespace or its definition are expected to become an
       integral and/or normative element of a standard being developed
       in the IETF or some other recognized standards body, that
       intention should be noted in this section.




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7.3.2.  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 quotes).

   3.  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 specific 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.)

   4.  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
       Section 2.1 of the URI specification [RFC3986].

7.3.3.  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.,
       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



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       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.

7.3.4.  Security and Privacy

   The "Security and Privacy" 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].

7.3.5.  Interoperability

   The "Interoperability" section MUST specify any potential issues
   related to interoperability.  Examples include possible confusion
   with other URN namespaces or naming systems because of syntax (e.g.,
   percent-encoding of certain characters) or scope (e.g., overlapping
   areas of interest).  If at all possible, concerns that arise during
   the registration of a URN namespace (e.g., due to the syntax or scope
   of an identifier system) SHOULD be resolved as part of the
   registration process.








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7.3.6.  Resolution

   The "Resolution" section MUST specify whether resolution mechanisms
   are intended or anticipated for URNs assigned within the namespace
   (e.g., URNs within some namespaces are intended to act as abstract
   designators and thus are not intended to be resolved).

   If resolution is intended, then this section SHOULD specify whether
   the organization that assigns URNs within the namespace intends to
   operate or recommend any resolution services for URNs within that
   namespace.  In addition, if the assigning organization intends to
   implement registration for publicly advertised resolution services
   (for example using a system based on principles similar to those
   described in [RFC2276] and [RFC2483]), then this section SHOULD list
   or reference the requirements for being publicly advertised by the
   assigning organization.

8.  IANA Considerations

8.1.  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 "[ this document ]" with "RFC"
   and 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 of [ this document ].

   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 7.3.4 and Section 9 of [ this
      document ].



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   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.

8.2.  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 (see especially Section 7).  In all cases, the IANA ought
   to assign the appropriate NID (formal or informal) once the
   procedures outlined in this document have been completed.

9.  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 7.3.4 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.

10.  References

10.1.  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.

   [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.





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   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

10.2.  Informative References

   [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>.

   [I-D.ietf-urnbis-semantics-clarif]
              Klensin, J., "URN Semantics Clarification", draft-ietf-
              urnbis-semantics-clarif-01 (work in progress), February
              2015.

   [ISO3166-1]
              ISO, "Codes for the representation of names of countries
              and their subdivisions -- Part 1: Country codes", ISO
              3166-1:2013, 2013.

   [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.

   [RFC2483]  Mealling, M. and R. Daniel, "URI Resolution Services
              Necessary for URN Resolution", RFC 2483, January 1999.

   [RFC3044]  Rozenfeld, S., "Using The ISSN (International Serial
              Standard Number) as URN (Uniform Resource Names) within an
              ISSN-URN Namespace", RFC 3044, January 2001.

   [RFC3187]  Hakala, J. and H. Walravens, "Using International Standard
              Book Numbers as Uniform Resource Names", RFC 3187, October
              2001.

   [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.

   [RFC5013]  Kunze, J. and T. Baker, "The Dublin Core Metadata Element
              Set", RFC 5013, August 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.

   [RFC7282]  Resnick, P., "On Consensus and Humming in the IETF", RFC
              7282, June 2014.

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

   [UNICODE]  The Unicode Consortium, "The Unicode Standard", 2015-,
              <http://www.unicode.org/versions/latest/>.

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








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   [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>.

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 7.3.1 of this document.

A.6.  Syntax

   Described under Section 7.3.2 of this document.  Unless the
   registration explicitly says otherwise, use of p-, q-, and/or
   f-components is not allowed for this namespace.



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A.7.  Assignment

   Described under Section 7.3.3 of this document.

A.8.  Security and Privacy

   Described under Section 7.3.4 of this document.

A.9.  Interoperability

   Described under Section 7.3.5 of this document.

A.10.  Resolution

   Described under Section 7.3.6 of this document.

A.11.  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.12.  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  Formally registers 'urn' as a URI scheme.

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

   o  Allows the "/", "~", and "&" characters in the namespace-specific
      string (NSS).

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

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 7.2.




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   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 [RFC3552] and
   privacy [RFC6973] issues 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.

   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, Henry S. Thompson, 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 and Melinda
   Shore in their roles as working group co-chairs 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.





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   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.

   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.

F.2.  Changes from -09 to -10

   o  Several clarifying editorial changes, most suggested by Ted Hardie
      and Henry S. Thompson (some of them off-list).

   o  Added a large number of placeholders that identify issues that
      require WG consideration and resolution (or WG delegation to the
      editors).

F.3.  Changes from -10 to -11

   o  Removed most of the placeholders added in -10.  Supplied new text
      as required or suggested by on-list discussion of those issues.

   o  Replaced the conformance examples Section 4.2 with a more complete
      collection and discussion.

   o  Revised and consolidated the registration procedure, and added
      provisions for NIDs that are the subject of standards and for
      avoiding race conditions about NID strings.





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   o  In response to independent comments from Ted Hardie and Henry S.
      Thompson, called attention to the possibility of conflicts between
      NID strings and various claims of national, corporate, and other
      perogatives.

   o  Changed the production for assigned-name as suggested by Lars
      Svensson.

   o  Several clarifying editorial changes including correcting a glitch
      in instructions to the RFC Editor.

F.4.  Changes from -11 to -12

   o  Removed p-components as a standalone construct, and instead folded
      them into the NSS.

   o  Defined syntax for r-components as a way to pass information to
      resolvers, but left the semantics for future standardization
      efforts.

   o  Further tuned the discussion of interoperability and related
      registration issues.

   o  Made a number of editorial corrections and reorganized the syntax
      material in Section 3 somewhat to make it internally consistent
      and keep the relationship to RFC 3986 clear.

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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