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Network Working Group                                        L. Masinter
Internet-Draft                                                     Adobe
Intended status: Informational                          October 22, 2010
Expires: April 25, 2011


         The 'tdb' and 'duri' URI schemes, based on dated URIs
                      draft-masinter-dated-uri-07

Abstract

   This document defines two URI schemes.  The first, 'duri' (standing
   for "dated URI"), allows indicating a URI as of a particular date
   (and time).  This allows explicit reference to the "time of
   retrieval", similar to the way in which bibliographic references
   containing URIs are used.

   The second scheme, 'tdb' ( standing for "Thing Described By"),
   provides a way of using a way of minting URIs for anything that can
   be described, with the ability to fix the description to a given date
   or time.  The 'tdb' URI scheme may reduce the need to define define
   new URN namespaces merely for the purpose of creating stable
   identifiers for concepts or abstractions: it provides a ready means
   for identifying "non-information resources" by semantic indirection
   -- a way of creating a URI for anything.

Note

   This document is not a product of any working group.  Many of the
   ideas here have been discussed since 2001.  This document has been
   discussed on the mailing list <uri@w3.org>.  Previous versions have
   couched 'tdb' and 'tdb' as URN namespaces.

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."




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   This Internet-Draft will expire on April 25, 2011.

Copyright Notice

   Copyright (c) 2010 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



































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Table of Contents

   1.  Overview and Requirements  . . . . . . . . . . . . . . . . . .  4
     1.1.  Persistent identifiers . . . . . . . . . . . . . . . . . .  4
     1.2.  URIs for abstractions  . . . . . . . . . . . . . . . . . .  5
   2.  Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.1.  'duri' Syntax  . . . . . . . . . . . . . . . . . . . . . .  6
     2.2.  tdb Syntax . . . . . . . . . . . . . . . . . . . . . . . .  6
     2.3.  encoded-URI encoding . . . . . . . . . . . . . . . . . . .  6
     2.4.  Timestamp syntax . . . . . . . . . . . . . . . . . . . . .  6
   3.  Semantics  . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.1.  'duri' Semantics . . . . . . . . . . . . . . . . . . . . .  7
     3.2.  'tdb' Semantics  . . . . . . . . . . . . . . . . . . . . .  7
     3.3.  Timestamp Semantics  . . . . . . . . . . . . . . . . . . .  8
   4.  Use as a Locator . . . . . . . . . . . . . . . . . . . . . . .  9
   5.  Hierarchy  . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   6.  Additional Considerations  . . . . . . . . . . . . . . . . . .  9
     6.1.  Embedded URI schemes . . . . . . . . . . . . . . . . . . .  9
     6.2.  Useful timestamps  . . . . . . . . . . . . . . . . . . . . 10
     6.3.  Free assignment  . . . . . . . . . . . . . . . . . . . . . 11
     6.4.  Resolution . . . . . . . . . . . . . . . . . . . . . . . . 11
     6.5.  Why Names with Semantics?  . . . . . . . . . . . . . . . . 11
     6.6.  Avoiding MetaData  . . . . . . . . . . . . . . . . . . . . 11
     6.7.  Avoiding 'duri' and 'tdb'  . . . . . . . . . . . . . . . . 12
     6.8.  'tdb' and levels of indirection  . . . . . . . . . . . . . 12
   7.  URI Specification Templates  . . . . . . . . . . . . . . . . . 13
     7.1.  'duri' Scheme Template . . . . . . . . . . . . . . . . . . 13
     7.2.  tdb Scheme Template  . . . . . . . . . . . . . . . . . . . 13
   8.  IANA considerations  . . . . . . . . . . . . . . . . . . . . . 14
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 15
     11.2. Informative References . . . . . . . . . . . . . . . . . . 15
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15
















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1.  Overview and Requirements

   The URI schemes defined here address several related problems:

1.1.  Persistent identifiers

   [RFC1737] defines several requirements for Uniform Resource Names.
   In particular, it requires "persistence":

      Persistence: It is intended that the lifetime of a URN be
      permanent.  That is, the URN will be globally unique forever, and
      may well be used as a reference to a resource well beyond the
      lifetime of the resource it identifies or of any naming authority
      involved in the assignment of its name.

   Many people have wondered how to create globally unique and
   persistent identifiers.  There are a number of URI schemes and URN
   namespaces already registered.  However, an absolute guarantee of
   both uniqueness and persistence is very difficult.

   In some cases, the guarantee of persistence comes through a promise
   of good management practice, such as is encouraged in "Cool URLs
   don't change" [COOL].  However, relying on promise of good management
   practice is not the same as having a design that guarantees
   reliability independent of actual administrative practice.

   A primary design goal for URIs is that they are intended to mean the
   same thing, no matter in what context they appear: a "Uniform" way to
   Identify a Resource.  However, even when URIs have Uniform meaning
   from the point of view of the source of the reference, they don't
   guarantee stability over time.  Despite best efforts and intentions,
   identifying information can change in unpredictable ways: domain
   names can disappear or be reassigned, name assigning organizations
   can change structure, responsibility, disappear, merge, or change in
   unpredictable ways.

   There is a significant dependence in the interpretation of many URNs
   with the concept of "naming authority".  The authority is presumably
   some individual or organization both to insure uniqueness of
   assignment and also to help with understanding the meaning of the
   link between the name and the named.

   However, authorities, whether individuals or organizations, have a
   lifetime, and must be consulted at some point to understand the
   bindings.  The functioning of names as unique identifiers and holders
   of meaning depends on having a reliable infrastructure of consulting
   the authority or the authorities records to determine the thing
   referenced.



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1.2.  URIs for abstractions

   The description of URIs [RFC3986] describes a range for 'Resource'
   that is quite broad:

      This specification does not limit the scope of what might be a
      resource; rather, the term "resource" is used in a general sense
      for whatever might be identified by a URI.  Familiar examples
      include an electronic document, an image, a source of information
      with a consistent purpose (e.g., "today's weather report for Los
      Angeles"), a service (e.g., an HTTP-to-SMS gateway), and a
      collection of other resources.  A resource is not necessarily
      accessible via the Internet; e.g., human beings, corporations, and
      bound books in a library can also be resources.  Likewise,
      abstract concepts can be resources, such as the operators and
      operands of a mathematical equation, the types of a relationship
      (e.g., "parent" or "employee"), or numeric values (e.g., zero,
      one, and infinity).

   One might use a URI such as "mailto:" email address to identify a
   person, or a "http:" URI to identify an abstract comment.  However,
   this leaves the question of how one might identify, within the same
   context, both the system mailbox and the person to which it is
   assigned, or the web page at a http URI and the concept it describes.
   The 'tdb' URI scheme allows ready assignment of URIs for abstractions
   that are distinguished from the media content that describes them.

   The goal, then, of the 'tdb' URI scheme is to provide a mechanism
   which is, at the same time:

      permanent: The identity of the resource identified is not subject
      to reinterpretation over time.

      explicitly bound: The mechanism by which the identified resource
      can be determined is explicitly included in the URI.

      useful for non-networked items: Allows identification of resources
      outside the network: people, organizations, abstract concepts.

      no administration: The mechanism does not depend on reliable
      administrative processes of authorities for either assignment or
      interpretation.


2.  Syntax






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2.1.  'duri' Syntax

   A 'duri' URI takes the form:
        duri:<timestamp>:<encoded-URI>

   where <timestamp> is s sequence of digits representing a date and
   time (Section 2.4) and <encoded-URI> is an absolute URI-reference
   [RFC3986] in which any reserved character other than "/" have been
   percent-encoded (Section 2.3).  Note that the URI which has been
   encoded MAY include a fragment identifier.

2.2.  tdb Syntax

   A 'tdb' URI takes a similar form:
        tdb:<timestamp>:<encoded-URI>

   with the same syntax.

2.3.  encoded-URI encoding

   The following characters must be encoded within <encoded-URI>:

   o  The character "#"
      Note that the URI encoded by <encoded-URI> can include a fragment
      identifier; the "#" character used to delimit it must be encoded.
      This feature is intended for use with 'tdb', where the fragment
      identified might contain the description.  Including an encoded
      "#" with a 'duri' is not as useful, since the fragment identifier
      might as well be applied to the 'duri' itself.

   o  The character "%"
      The encoded-URI can itself contain encoded characters, which are
      encoded with the same method.  To insure that decoding happens at
      the right level of processing, the "%" itself must be encoded.
      Unfortunately, this means there are cases where there is a double
      encoding of characters, first to construct the embedded URI itself
      and second to then embed the URI within the 'tdb' or 'duri' URI.

2.4.  Timestamp syntax

   A timestamp in these URI schemes consists of a restricted subset of
   date times, as per [RFC3339].  The goal is to allow relatively short
   expressions with no ambiguity, but also with arbitrary precision.

     timestamp = date [ "T" time "Z" ]
     date       =date-fullyear [ "-" date-month [ "-" date-mday ]]
     time       = time-hour  [ ":" time-minute
                  [ ":" time-second [ time-secfrac ]]]



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   where non-terminals "date-fullyear", "date-month", "date-mday",
   "time-hour", "time-minute", "time-second", "time-secfrac" are taken
   from [RFC3339].  The goal was to minimize the amount of precision
   needed, while retaining the possibility of generating timestamps that
   are exactly compatible with [RFC3339] "date-time" non-terminal.


3.  Semantics

3.1.  'duri' Semantics

   It is traditional in convention references and citations in printed
   works to include the date of publication; this practice serves the
   important purpose that the context of the naming can be determined.

   The meaning of a 'duri' URI is "the resource that was identified by
   the <encoded-URI> (after hex decoding) at the date(time) given".

   For example, "duri:2001:http://www.ietf.org" is a persistent
   identifier to "http://www.ietf.org" as of 2001.  A 'duri' URI may not
   be a resource locator in a practical sense: the time of location has
   not yet arrived or has passed.

3.2.  'tdb' Semantics

   The 'tdb' URI scheme is intended to be useful for describing
   entities, concepts, abstractions, and other items which may not
   themselves be network accessible resources, but have been at some
   point described by network accessible resources.

   A 'tdb' URI is intended to be used where the <encoded-URI> identifies
   a 'document' (something a person could read, peruse, understand) or a
   fragment thereof, where the document describes some thing or concept.
   The 'tdb' URI itself then identifies the subject of that document.
   It is common practice to give a reference for a concept by including
   a pointer to a document, segment, phrase that defines the concept;
   'tdb' attempts to capture this practice in URI space.

   For example, one might use "tdb:2008:http://www.ietf.org" as a
   persistent identifier for the Internet Engineering Task Force, as
   described by the "http://www.ietf.org" in 2008.

   The 'tdb' URI scheme differs from other URI or URN methods for
   identifying abstractions because the designation of what is actually
   identified by the 'tdb' doesn't depend on knowing the intention of
   the "assigner" of the identifier.  Unlike "tag", "info", "cid", "mid"
   or related schemes, the identification is not dependent on the
   context of use.  The 'tdb' URI scheme can be thought of as giving a



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   way to invoke a level of semantic indirection to URI resolution.

   While one could imagine using 'tdb' without a date, it would leave
   the possibility that a reference that is unambiguous at one time
   might become ambiguous at some other time.  There are two ways that
   the date is useful for 'tdb' URIs: it fixes the time of access of the
   resource, for variable descriptions, and it fixes the time of
   interpretation, for descriptions whose meaning (in natural language)
   might vary.

3.3.  Timestamp Semantics

   It is traditional in convention references and citations in printed
   works to include the date of publication; this practice serves the
   important purpose that the context of the naming can be determined.

   While one could imagine using 'tdb' without a timestamp, it would
   leave the possibility that a reference that is unambiguous at one
   time might become ambiguous at some other time.  There are two ways
   that the date is useful for 'tdb': it fixes the time of access of the
   resource, for variable descriptions, and it fixes the time of
   interpretation, for descriptions whose meaning (in natural language)
   might vary.  While normally, in a literary work in natural language
   which makes a reference to another work, both the reference itself
   and the work referenced are dated, e.g., a footnote in an article
   written in 1967 might talk about a "private communication" which
   itself had a date.  The difference between a URI and a conventional
   literary reference is the desire to be able to extract the URI from
   its context and still retain its meaning.

   The meaning of a timestamp is the interval specified by the
   granularity of the time range indicated, in the UTC time zone, as
   described in [RFC3339].  If necessary, timestamps can include times
   and even fractional times, so that a generator of 'duri' or 'tdb'
   URIs can be arbitrarily precise.

   If there is any ambiguity of the resource within the range of time
   indicated (for example, if the timestamp consists only of a year, and
   the resource changes over the course of the year), then the resource
   state as of the very last instant of the range indicated should be
   used.

   Timestamps are allowed to be specified with as much precision as
   needed.  This keeps most 'duri' and 'tdb' URIs relatively short.







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4.  Use as a Locator

   A 'duri' URI is not directly useful as a resource locator, since many
   resources vary their content over time.

   A 'tdb' URI is not a resource locator in a practical sense, since it
   explicitly requires human interpretation.  However, it allows one to
   know that a resource was described at some point in time; whether the
   description is still available, or whether that description is still
   meaningful, is not guaranteed.


5.  Hierarchy

   For 'tdb', the "thing described by" a resource may bear little
   relationship to the "thing described by" a relative pointer, so the
   'tdb' URI scheme seems to have no use cases for using "/" as a
   hierarchical delimiter.

   However, 'duri' URIs can often be used with relative URI references
   with some amount of reliability.  Note, however, that double-encoding
   of previously encoded URI characters will cause some problems.


6.  Additional Considerations

6.1.  Embedded URI schemes

   The intent of 'duri' and 'tdb' is to use them with embedded URI
   references that identify documents or document fragments.  That is,
   they are most useful for "information resources".

   For example, use with a "http" URI can be used to refer to a web page
   or the subject of a web as it was described at the given time.  This
   can be a way of referring to a web site at some time in the past, or
   an organization that has changed, merged, split, or disappeared.

   Local systems that have known-to-be unique host names can use "file"
   URIs with 'tdb', for example,

       tdb:20010814142327:file://this.example.com/c|/temp/test.txt

   since this use is primarily focused on providing a unique way of
   identifying an abstraction, even if the referent of the abstraction
   is not widely known.  (Using 'file:' URIs in this way without a fully
   qualified domain name would not be appropriate, because the
   interpretation is not uniform.)




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   One might consider using 'tdb' with a "data" URI to designate
   concepts that can be described uniquely briefly inline.  For example,

        tdb:2001:data:,The%20US%20president

   names the concept described by the (text/plain) string "The US
   president" at the very last instant of 2001.  Of course, this
   practice is only useful if the referent of the data is (or was at the
   time) completely unique.  Since "data" does not contain a way to
   designate content-language, the string in question would have to not
   be ambiguous as to its language.  In the case of 'data', there is no
   assigning authority at all; the interpretation of the 'tdb' depend on
   the interpreting community.

   Using 'tdb' or 'duri' with an embedded 'urn:' might not seem to be
   too useful, But it might be useful where the assignment of names in a
   URN namespace are not, in practice, permanent, or that one might want
   to refer to the assignment as of a given date.  In this case, it is
   possible to use a "urn" within a 'duri', e.g.,

         duri:2000:urn:ietf:std:50

   might be used to refer to "the document that the IETF considered to
   be STD 50, as of the last instant of 2000".

   For 'tdb', many URIs identify resources which do not clearly describe
   anything at all.  The "home page" for an organization isn't nearly as
   good a resource to use to describe an organization as the
   organization's "about" page.  But it is up to the minter of the 'tdb'
   URI to choose wisely.

6.2.  Useful timestamps

   Timestamps far in the future are suspect, because the future content
   of a description resource cannot usually be reliably predicted.
   Timestamps which preceed the availability of the description resource
   should not be used either.  For example, using a http URI with a
   timestamp before the description resource is also not recommended.

   However, although these practices are not recommended, there is no
   assurance that they haven't been used; by itself, a 'tdb' URI by
   itself does not constitute an assertion that the description resource
   was available or assigned at the date specified.

   Note that the use of the "very last instant" allows for the
   conventional bibliographic convention that a work published in 2009
   can use "2009" as the date string, to refer to the work in the year
   of publication.



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6.3.  Free assignment

   Because of the many possible schemes that can be used in the
   <encoded-URI> portion, there should be no difficulty in almost any
   computational process being able to assign 'duri' or 'tdb' URIs at
   will.  Of course, it is necessary for there to be some resource which
   is available at some point in time, and to have a clock which is
   accurate to the granularity of the frequency of assignment.

6.4.  Resolution

   There are no direct resolution servers or processes for 'duri' or
   'tdb' URIs.  However, a 'duri' URI might be "resolvable" in the sense
   that a resource that was accessed at a point in time might have the
   result of that access cached or archived in an Internet archive
   service.  See, for example, the "Internet Archive" project [archive].
   And a 'tdb' URI is "resolvable" in the sense that the description
   resource can be accessed and interpreted.

   Clients without access to an Internet archive service might take the
   decoded <encoded-URI> of a 'duri' and attempt resolution of *that*
   identifier.  This will give an approximation whose reliability
   depends on the what has happened in the time since the date
   indicated.

6.5.  Why Names with Semantics?

   There are a number of URI and URN schemes that create otherwise
   unbound "names", where the scheme only provides for uniqueness, with
   some other agent or process or context providing the authority to
   interpret the meaning of the identifier at some point in the future.
   'duri' and 'tdb' is different, in that it is the agreement between
   the describer (the agent creating the URI) and the receiver of the
   URI (the agent interpreting the URI) to agree upon the semantics
   without any reference to any third party.

6.6.  Avoiding MetaData

   One might consider the timestamp in a 'duri' or 'tdb' URI to be just
   one piece of additional metadata about the URI, and consider adding
   other pieces of metadata as annotation.

   However, the use of the timestamp is intended primarily as a
   mechanism of accomplishing uniqueness over time.  No other bit of
   metadata or description readily fills that purpose.  Further, the
   date is not descriptive (an assertion about the URI) but merely
   refining.




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6.7.  Avoiding 'duri' and 'tdb'

   Many applications of URIs already provide a context of timestamp.
   For example, one could imagine a hypertext system where the URIs
   contained within a document were intended to refer to the resources
   as of the date of the enclosing document.  This would be a reasonable
   interpretation of URIs within an Internet archive system, for
   example.

   Some applications of URIs already implicitly use the level of
   interpretive indirection that is explicit with 'tdb', For example,
   within an ontology language definition, the URIs used for abstract
   concepts, individuals and so forth are generally considered the
   "thing described by" the URI.

   In addition, the 'application/rdf+xml' Media Type [RFC3870] uses the
   fragment identifier resolution as an explicit way of identifying
   abstract concepts that are described by an RDF document.

6.8.  'tdb' and levels of indirection

   The 'tdb' scheme introduces a level of semantic indirection.  The
   puzzles and confusions about use and mention, name and reference, and
   levels of indirection have been puzzling and amusing for quite a
   while.

      "It's long," said the Knight, "but it's very, very beautiful.
      Everybody that hears me sing it--either it brings tears into their
      eyes, or else--"
      "Or else what?" said Alice, for the Knight had made a sudden
      pause.
      "Or else it doesn't, you know.  The name of the song is called
      'Haddock's Eyes.'"
      "Oh, that's the name of the song, is it?"  Alice said, trying to
      feel interested.
      "No, you don't understand," the knight said, looking a little
      vexed.  "That's what the name is called.  The name really is 'The
      Aged Aged Man.'"
      "Then I ought to have said 'That's what the song is called'?"
      Alice corrected herself.
      "No, you oughtn't: that's quite another thing!  The song is called
      'Ways and Means': but that's only what it's called, you know!"
      "Well, what is the song, then?" said Alice, who was by this time
      completely bewildered.
      "I was coming to that," the Knight said.  "The song really is
      'A-sitting On A Gate': and the tune's my own invention."  [LOOK]





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7.  URI Specification Templates

7.1.  'duri' Scheme Template

   URI scheme name:  duri

   Status:  permanent

   URI scheme syntax:  Briefly, the syntax is
      tdb:<timestamp>:<encoded-URI>
      The syntax is described in this document.

   URI scheme semantics:  A URI as of a particular time.  Semantics are
      described in detail in this document.

   Encoding considerations:  'duri' URIs consist of a prefix followed by
      another URI, and should have the same encoding considerations as
      others.  Note discussion of double-encoding.

   Applications/protocols that use this URI scheme name:  Limited: this
      scheme was originally developed as a "thought experiment",
      although there is some discussion of using it with Memento
      [MEMENTO].

   Interoperability considerations:  The actual interoperability with
      Internet archiving services needs further exploration.

   Security considerations:  See Section 9 of this document.

   Contact:  Larry Masinter tdb:2010:http://larry.masinter.net

   Author/Change controller:  as above

   References:  See References of this document.

7.2.  tdb Scheme Template

   URI scheme name:  tdb

   Status:  permanent

   URI scheme syntax:  Briefly, the syntax is
      tdb:<timestamp>:<encoded-URI>
      The syntax is described in this document.







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   URI scheme semantics:  Semantic indirection at indicated date.
      Semantics are described in detail in this document.

   Encoding considerations:  'tdb' URIs consist of a prefix followed by
      another URI, and should have the same encoding considerations as
      others.  Note discussion of double-encoding possibilities.

   Applications/protocols that use this URI scheme name:  Limited: This
      scheme was originally designed as a "thought experiment", as a way
      resolve some of the use/mention ambiguities in semantic web
      applications that wish to "denote" concepts and other ideas and
      not just access resources over the Internet.

   Interoperability considerations:  Existing semantic web applications
      may have other means of fixing meaning at a particular time or
      semantic indirection, and do not fix description by time.

   Security considerations:  See Section 9 of this document.

   Contact:  Larry Masinter tdb:2010:http://larry.masinter.net

   Author/Change controller:  as above

   References:  See References of this document.


8.  IANA considerations

   This document includes two URI scheme registrations (Section 7 that
   should be entered into the IANA registry of URI schemes as a
   permanent registration (once approved).


9.  Security Considerations

   'tdb' identifiers are not any more reliable because they have dates.
   URIs don't contain enough information to supply the authority for
   deciding what was or wasn't at a given URI at a given date.


10.  Acknowledgements

   There have been many discussions over several years on the
   relationship of URLs, URNs, URIs, resources and resource identifiers,
   with many contributions.  Particular thanks to Alfred Hines, Herbert
   Van de Sompel, Al Gilman, Aaron Swartz, Brian McBride, Stuart
   Williams, Michael Mealling, Ray Denenberg and Pat Hayes.




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11.  References

11.1.  Normative References

   [RFC3339]  Klyne, G. and C. Newman, "Date an Time on the Internet:
              Timestamps", RFC 3339, July 2002.

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

   [namespaces]
              Bray, T., Hollander, D., and A. Layman, "Namespaces in
              XML", W3C Recommendation REC-xml-names, January 1999,
              <http://www.w3.org/TR/REC-xml-names>.

11.2.  Informative References

   [COOL]     Berners-Lee, T., "Cool URIs don't change", 1998,
              <http://www.w3.org/Provider/Style/URI.html>.

   [LOOK]     Carroll, L., "Through the Looking Glass", 1872, <http://
              www.literature.org/authors/carroll-lewis/
              through-the-looking-glass/chapter-08.html>.

   [MEMENTO]  Memento Development Group, "Memento: Adding Time to the
              Web", 2010, <http://mementoweb.org/>.

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

   [RFC3870]  Swartz, A., "application/rdf+xml Media Type Registration",
              RFC 3870, September 2004.

   [archive]  Kahle, B., "Preserving the Internet", Scientific
              American , March 1997,
              <http://www.sciam.com/0397issue/0397kahle.html>.














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Author's Address

   Larry Masinter
   Adobe
   345 Park Ave
   San Jose, CA  95110
   US

   Phone: +1 408 536 3024
   Email: LMM@acm.org
   URI:   http://larry.masinter.net








































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