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Versions: 00 01 draft-ietf-urnbis-semantics-clarif

Uniform Resource Names (urnbis)                             J.C. Klensin
Internet-Draft                                             April 7, 2014
Updates: 3986 (if approved)
Intended status: Standards Track
Expires: October 07, 2014

              Names are Not Locators and URNs are Not URIs


   Experience has shown that identifiers associated with persistent
   names are quite different from identifiers associated with the
   locations of objects.  This is especially true when such names are
   are expected to be stable for a very long time or when they identify
   large and complex entities.  In order to allow Uniform Resource Names
   (URNs) to evolve to meet the needs of the Informational Sciences
   community and other users, this specification separates the syntax
   for URNs from the generic syntax for Uniform Resource Identifiers
   (URIs) specified in RFC 3986, updating the latter specification

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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   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on October 07, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Simplified BSD License.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  A perspective on locations and names . . . . . . . . . . . . .  2
   3.  Changes to RFC 3986  . . . . . . . . . . . . . . . . . . . . .  5
   4.  Other Required Actions . . . . . . . . . . . . . . . . . . . .  5
   5.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  5
   6.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . .  5
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  6
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . .  6
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     9.1.  Normative References . . . . . . . . . . . . . . . . . . .  6
     9.2.  Informative References . . . . . . . . . . . . . . . . . .  6
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . .  6

1.  Introduction

   The Internet community now has many years of experience with both
   name-type identifiers (notably Uniform Resource Names (URNs [RFC2141]
   [RFC2141bis]) and location-based identifiers (notably Uniform
   Resource Locators (URLs) [RFC1738]).  That experience leads to the
   conclusion that it is impractical to constrain URNs to the syntax and
   high-level semantics of URLs.  Generalization from URLs to generic
   Uniform Resource Identifiers (URIs) [RFC3986], especially to name-
   based, high-stability, long-persistence, identifiers of the URN
   variety, has failed because the assumed similarities do not exist to
   a sufficient degree.  Ultimately, locators, which typically depend on
   particular accessing protocols and a specification relative to some
   physical space or network topology, are simply different creatures
   from long-persistence, location-independent, object identifiers.  The
   syntax and semantic constraints that are appropriate for locators are
   either irrelevant to or interfere with the needs of resource names as
   a class.  That was tolerable as long as the URN system didn't need
   additional capabilities but experience since RFC 2141 was published
   has shown that they are, in fact, needed.

   This specification updates the Generic URI Syntax specification
   [RFC3986] to exclude URNs from its coverage.  Put differently, with
   the publication of this specification, URNs are no longer considered
   a member of the class of URIs to which RFC 3986 applies.

   [[Note in draft: the above leaves it ambiguous as to whether it
   remains appropriate to call URNs "URIs".  That ambiguity is
   intentional and, if possible should keep the question part of the
   "someone else's problem" category.]]

   For URLs and such other URIs as may exist or be created in the
   future, this specification does not change the syntax rules and other
   requirements and recommendations of RFC 3986.

2.  A perspective on locations and names

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   Content industries (e.g., publishers) and memory organizations (e.g.,
   libraries, archives, and museums) invest a lot of resources on naming
   things and the topics of naming and classification are important
   information science issues.  Tens, if not hundreds, of millions of
   persistent identifiers have been assigned during the last decade.

   Several identifier systems have been developed for persistent and
   unique identification of resources.  When there is a real need to
   preserve something important (such as scientific publications,
   research data, government publications, etc.) for the long term, URNs
   or other persistent identifiers are used; URLs (or other generic
   URIs) are not being used for identification or even linking purposes.

   Naming and locating e.g.  library resources are both complex
   activities which have different aims.  Traditionally, naming and
   locating resources have been separate activities, and the rules for
   the former are much more stringent than for the latter.  The same
   principles are being applied to digital materials as well as more
   traditional ones.  In a library, any book, be it printed or digital,
   has both unique and persistent International Standard Book Number
   (ISBN) and non-unique (each copy has its own location information)
   and short-lived location information which cannot be trusted in the
   long run.  ISBN never changes, but both shelf locations and Web
   addresses usually do, many times during the book's life span.

   Giving location information a role in identification would not only
   force libraries to adopt different policies for printed and digital
   content, it would also undermine the value of existing identifier
   systems.  Let us assume that ten people independently upload a copy
   of an electronic book into different locations in the Web.  Are all
   these ten URLs valid identifiers of the book?  And what is their
   relation to the ISBN or other identification information of the book
   such as its title?

   From the perspective of the communities who depend on persistent
   identifiers, critical issues include:

   1.  Resource identification has to be a managed process.  Assigning
       URIs generally  is not.  Although it may be possible to introduce
       some level of control to URI assignment, a user cannot determine
       whether some URI is reliable or not.

   2.  Anyone may assign new URIs to resources even if these resources
       already have proper identifiers assigned to them.  Claiming that
       these URIs actually identify something undermines the value of
       proper identifiers.

   3.  There is no 1:1 relation between the resource identified and
       URIs.  An e-book in the Web may be represented as 1-n files
       (URIs), and a single file may contain several books.  And books
       are simple, we need to name very complex objects such as research
       data sets, or some component parts within these complex data

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   4.  One resource such as a scientific article is typically available
       from multiple locations, including (for instance) the publisher's
       document supply service, a university's open repositories and
       other cooperative repository systems, legal deposit collections
       and the Internet archive.  A resource should have one and only
       one identifier of a given type; URIs do not meet this

   5.  URIs relate to instances (copies) of resources, whereas
       traditionally identification has much broader scope.  Identifiers
       may be assigned to, e.g., an immaterial work (such as Hamlet),
       its expressions (e.g.  Finnish translation of Hamlet), and
       manifestations of works and expressions (e.g.  PDF version of
       Finnish translation of Hamlet).

   6.  Over time, different resources (or different versions of the same
       resource) may be found from the same non-URN URI.  A user has no
       way of knowing whether the resource has changed.  One of the
       basic principles for proper identifier systems is that the same
       identifier is never assigned to another resource.  In general,
       URIs do not meet this requirement.

   7.  Persistent identification must be available for resources which
       are available only in databases and other environments that are
       often identified today as "deep web".  URIs for these resources
       tend to be very complicated and it will be difficult to keep them
       alive even with the help of DNS redirection when e.g.  the
       underlying database management system changes.

   8.  The role URI fragment and query could or should have in
       identification is unclear and the statements in RFC 3986 are
       definitely problematic from the points of view of existing
       identifier systems and management of naming.

   Does fragment identify a location or a certain section of a resource?
   In the evolving set of URN Internet standards, fragment will not be a
   part of the Namespace Specific String.  Then fragment only indicates
   a place / segment within the identified resource, but does not
   identify it.  If fragment had a role in identification, fragments
   would extend the scope of existing standard identifiers to component
   parts of resources.  For instance, anyone could use URN based on ISBN
   + fragment to identify chapters of electronic books.

   Things get even more complicated with query since what an identifier
   + query resolves to may not have anything to do with the original
   resource.  For instance, URN based in ISBN + query may resolve to the
   metadata record describing the book.  These records have their own
   identifiers which are not based on ISBNs.

   [[Note in draft: Most of the discussion above may belong in 2141bis
   rather than here.]]

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   9.  For many organizations, persistence means decades or centuries.
       Anything that is protocol dependent will eventually fail.  URLs
       do not change by themselves, but in the long run it is very
       difficult for people to not change them or the objects to which
       they point.

   The mention of centuries is intentional.  Content industries, memory
   organizations (such as national and repository libraries and national
   archives) and universities and other research organizations, need
   identifiers that will persist for hundreds of years.  Such
   identifiers might even need to outlast the institutions themselves,
   and definitely should be usable even if current technologies such as
   the Web and the Internet cease to exist or are supplanted by
   something new (as unlikely as that might seem today).

   In addition, operations on, or additional specifications about, names
   and the associated objects must be possible, as stable as the names
   themselves, and reasonably efficient.  For example, if a URN were
   assigned to an encyclopedia that consisted of many volumes, it should
   be feasible to identify (and locate and retrieve if that were
   desired) a particular volume or even a particular article without
   accessing or retrieving the entire set.

3.  Changes to RFC 3986

   This specification removes URNs from the scope of RFC 3896.  It makes
   no changes for URI types that remain within that scope.

4.  Other Required Actions

   The basic URN syntax specification [RFC2141] was published well
   before RFC 3986 and therefore does not depend on it.  Successors to
   that specification will need to fully spell out the syntax and
   semantics of URNs without generic or implicit reference to any URI

5.  Acknowledgments

   This specification was inspired by a search in the IETF URNBIS WG for
   other alternatives that would both satisfy the needs of persistent
   name-type identifiers and still fully conform to the specifications
   and intent of RFC 3986.  That search lasted several years and
   considered many alternatives.  Discussions with Leslie Daigle, Juha
   Hakala, Barry Leiba, Keith Moore, Andrew Newton, and Peter Saint-
   Andre during the last quarter of 2013 and the first quarter of 2014
   were particularly helpful in getting to the conclusion that a
   conceptual separation of notions of location-based identifiers (e.g.,
   URLs) and the types of persistent identifiers represented by URNs was
   necessary.  Peter Saint-Andre provided significant text in a pre-
   publication review.

6.  Contributors

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   Juha Hakala contributed most of the text of Section 2.

      Contact Information:
   Juha Hakala
   The National Library of Finland
   P.O. Box 15, Helsinki University
   Helsinki, MA FIN-00014
   Email: juha.hakala@helsinki.fi

7.  IANA Considerations

   [[RFC Editor: Please remove this section before publication.]]

   This memo is not believed to require any action on IANA's part.  In
   particular, we note that there are a collection of "Uniform Resource
   Identifier (URI) Schemes" that does not include URNs and a series of
   URN-specific registries that do not rely on the URI specificstions.

8.  Security Considerations

   All drafts are required to have a security considerations section.

9.  References

9.1.  Normative References

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

   [RFC3986]  Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005.

9.2.  Informative References

              Mazahir, O., Thaler, D. and G. Montenegro, "Deterministic
              URI Encoding", February 2014, <http://www.ietf.org/id/

   [RFC1738]  Berners-Lee, T., Masinter, L. and M. McCahill, "Uniform
              Resource Locators (URL)", RFC 1738, December 1994.

              Saint-Andre, P., "Uniform Resource Name (URN) Syntax",
              January 2014, <https://datatracker.ietf.org/doc/draft-

Author's Address

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

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

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