Internet Info 1997 December/Internet_Info_CD-ROM_Walnut_Creek_December_1997.iso/ietf/urn/urn-archives/urn-ietf.archive.9610/000055_owner-urn-ietf _Fri Oct 18 13:50:23 1996.msg

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From: "Ryan Moats" <[e-mail]>
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Cc: "Leslie Daigle" <[e-mail]>,
        "Michael Mealling" <[e-mail]>,
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Subject: [URN] Pre release of URN Syntax document....
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Well folks, we've reached the point where this is ready for the list
to scream about (semi :-) ).

Have at it....

Ryan Moats
InterNIC Directory and Database Services
[e-mail]


===================================================







Internet-Draft                                                Ryan Moats
draft-ietf-urn-syntax-00.txt                                        AT&T
Expires in six months                                       October 1996


                               URN Syntax
                 Filename: draft-ietf-urn-syntax-00.txt


Status of This Memo

      This document is an Internet-Draft.  Internet-Drafts are working
      documents of the Internet Engineering Task Force (IETF), its
      areas, and its working groups.  Note that other groups may also
      distribute working documents as Internet-Drafts.

      Internet-Drafts are draft documents valid for a maximum of six
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      Coast), or ftp.isi.edu (US West Coast).


Abstract

   This document presents the syntax for Uniform Resource Names (URNs).
   More information on the purpose of URNs is available from [1].

1. Syntax

   All URNs have the following syntax:


   <URN> ::= ["urn:"] <NID> ":" <NSS>

   <NID> is the Namespace IDentifier, and <NSS> is the Namespace
   Specific String.  The Namespace ID is used to determine the
   _syntactic_ interpretation of the Namespace Specific String to the
   extent of extracting the Naming Authority information (as discussed
   in [1]).

   RFC 1737 [2] puts additional requirements on URN encoding, which all



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   have implications as far as limiting syntax.  On the other hand, the
   requirement to grandfather existing naming systems has the effect of
   broadening syntax.  Thus, we discuss the acceptable syntax for both
   the Namespace Identifier and the Namespace Specific String
   separately.

1.1 Namespace Identifier Syntax

   The following is the syntax for the Namespace Identifier. To (a) be
   consistent with all potential resolution schemes and (b) not put any
   undue constraints on any potential resolution scheme, the syntax for
   the Namespace Identifier is:

   <NID>         ::= <letter> [ <let-hyp> ]

   <let-hyp>     ::= <letter> | "-"

   <letter>      ::= any one of the 52 alphabetic characters A through Z
                     in upper case and a through z in lower case

   This is slightly more restrictive that what is stated in RFC 1738 [4]
   (which allows the period "."). Further, the Namespace Identifier is
   case insensitive, so that "ISBN" and "isbn" refer to the same
   namespace.

1.2 Namespace Specific String Syntax

   Depending on the rules governing a namespace, valid identifiers in a
   namespace might contain characters that are reserved characters in
   URI syntax or non-printable ASCII characters.  To accommodate the
   largest set of valid identifiers, the NSS portion of a URN shall use
   UTF-8 representation of ISO 10646 as its character set.

   Clients MUST be capable of %encoding the UTF-8 formatted NSS,
   according the rules in [3] with the following exceptions:

      1. [3] states that occurrence of the '/' character in URIs must
      denote hierarchy, so that partial forms of a URI are possible.
      This restriction is unenforceable, and relative URLs do not have a
      scheme prefix, so we allow URNs to contain unescaped occurrences
      of the '/' character that do not denote hierarchy.

      2. As an optimization when the transport between systems is known
      to be 8-bit-clean, clients MAY omit the %encoding on 8-bit
      characters but MUST still %encode the reserved characters below.

   For historic reasons, the characters "#", "?", "%", "*", "!", "<",
   ">", and '"', are reserved and must be encoded with '%'.  Thus client



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   implementers should accept URNs from users in an unencoded form but
   must encode them before sending them to a resolver.

   URN resolvers MUST be capable of accepting URNs that have been
   %encoded for either 8-bit clean or 7-bit transports.  %encoding is
   removed first, then UTF-8 decoding is performed.  URN resolvers MUST
   return identical results from ANY legally encoded form of the URN.

   It should be noted that certain characters in the Namespace Specific
   String syntax may have special meaning in certain namespaces.
   Therefore, each namespace shall indicate which characters have
   special meaning and how (if possible) to encode those characters if
   used in a literal sense.


2. Grand-fathering

   To allow for grand-fathering of existing naming systems (as required
   by [2]), the Namespace Specific String shall be considered an "opaque
   string" in the sense of structure except as mentioned in Section 1.

3. Lexical Equivalence

   As discussed previously, Namespace Identifiers are to be considered
   case-insensitive. That is, the following two URNs are lexically
   equivalent:

           urn:isbn:0-201-10174-2
           urn:ISBN:0-201-10174-2

   Lexical equivalence at the client is restricted to unencoding '%'
   sequences, with other comparisons being considered case sensitive.
   That is, the following two URNs are lexically equivalent at a client:

           urn:foo:John DeSilva
           urn:foo:John%20DeSilva

   but the following two URNs are NOT lexically equivalent at a client:

           urn:foo:John%20DeSilva
           urn:foo:John%20deSilva

   Lexical equivalence at the server is dependent on the namespace, and
   thus each namespace shall indicate how lexical equivalence may be
   determined by servers for URNs specifying resources in that
   namespace.





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4. Security considerations

   Because of the number of potential namespaces, it must be restated
   that certain of the characters in the Namespace Specific String may
   have special meaning to certain namespace resolvers.  Each namespace
   shall therefore indicate which characters have special meaning and
   how (if possible) to encode those characters if used in a literal
   sense.

5. Acknowledgments

   Thanks to various members of the URN working group and <<your name
   here!!>> for comments on earlier drafts of this document.  This work
   was partially supported by the National Science Foundation.

6. References

   Request For Comments (RFC) and Internet Draft documents are available
   from <URL:ftp://ftp.internic.net> and numerous mirror sites.

         [1]         L. L. Diagle, P. Falstrom, R. Iannella.  "A Frame-
                     work for the Assignment and Resolution of Uniform
                     Resource Names", Internet Draft (work in progress).
                     June 1996.


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


         [3]         T. Berners-Lee. "Universal Resource Identifiers in
                     WWW", RFC 1630. June 1994.


         [4]         T. Berners-Lee, L. Masinter, M. McCahill. "Uniform
                     Resource Locators (URL)", RFC 1738.  December 1994.

7. Author's address

   Ryan Moats
   AT&T
   15621 Drexel Circle
   Omaha, NE 68135-2358
   USA

   Phone:  [phone]
   EMail:  [e-mail]



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INTERNET DRAFT                 URN Syntax                   October 1996


                This Internet Draft expires April 1, 1997.


















































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