W3C home > Mailing lists > Public > uri@w3.org > April 2003

New Text for RFC 2396 intro, reframing what URIs are for

From: Sandro Hawke <sandro@w3.org>
Date: Wed, 23 Apr 2003 16:31:41 -0400
Message-Id: <200304232031.h3NKVf4n031409@roke.hawke.org>
To: uri@w3c.org
Cc: pat hayes <phayes@ai.uwf.edu>


Okay, I'm taking a stab at some new text for the introduction to
2396bis.  I haven't worked out the exact 'diff' details but I'm happy
to if it comes to that.  This text goes somewhere around section 1.1,
but if this slight reframing is accepted, I think some later sentences
will have to be rephrased.

I bravely/naively think this roughly meets the needs of all comers
(including the newcomers-to-this-list like Pat Hayes), and I'm sure
people will be happy to tell me where I'm wrong.  If this addresses
your needs better than the current text, a brief comment to that
effect would be appreciated.

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

1.  Being a URI
  
    A URI is a string which conforms to the URI syntax given in this
    document.  This restricted syntax serves several purposes:

              a.  It excludes certain characters.  This allows
	      systems to use those characters to delimit URIs.

	      b.  It defines each URI as beginning with a "scheme"
	      name followed by a colon.  This allows independent
	      development and deployment of systems which offer 
	      URIs additional semantics and functionality.

	      c.  It defines a few characters (including "/") to have
	      special "hierarchical" meaning, to allow for "relative"
	      URIs.

	      d.  It defines a character-escape mechanism (using "%")
	      to allow special characters (like "/") to be used as
	      normal characters, without their special URI meaning.

	      e.  It keeps them syntactically distinct from some other
	      short, formally-specified strings, so they can sometimes
	      be intermixed or used to flag an extension to a protocol
	      or when "webifying" systems.

2.  The Identification Function (RIF)

   There is a single relation, called the "RFC 2396bis
   identification function" ("RIF"), which maps from each URI to
   exactly one thing at any point in time.  Some shared knowledge of
   this relation is essentially to communcation using URIs, but
   complete shared knowledge is rarely possible.  The central efforts
   and standards related to URIs concern techniques for sharing
   knowledge of this relation sufficient for particular applications.

              a.  We call the objects in the range (set of possible
	      output values) of RIF "resources".  This term is not
	      intended to exclude anything and the range of RIF is in
	      no way restricted.  Every person, place, event, physical
	      object, imaginary character, ... anything and everything
	      is in the range of RIF and is technically a resource --
	      but calling something a "resource" suggests that it is
	      likely to be identified by a URI in practice.  For
	      example, the integer zero is technically a resource
	      (since everything is a resource), but calling it a
	      resource would be misleading outside of a context where
	      URIs were actually being used to denote integers.

	      [[ Thus RDF bNodes and literals can be said to identify
              resources, even if there is no URI in use, because
              assigning a URI would be reasonable and may happen
              automatically in some software. ]]

	      b.  Resources can be further divided into "bound
	      resources" and "unbound resources".  Bound resources are
	      in the codomain of RIF; they are in fact identifiable
	      through RIF from some URI.  Unbound resources are not in
	      the codomain of RIF and cannot be identified through the
	      RIF mapping from some URI.  Not all resources can be
	      bound because there are more resources than URIs.  Since
	      it may not be possible to know whether a given resource
	      is bound, the boundness distinction should be used with
	      care, or used with respect to a particular URI scheme as
	      in, "Since my new book does not yet have an ISBN, it is
	      an unbound resource with respect to the isbn: scheme."

	      [[ That's trying to address Mike Mealling's requirement.
	      http://lists.w3.org/Archives/Public/uri/2003Apr/0055 ]]
          
	      c.  Elements of RIF SHOULD NOT change over time, since
	      such changes will render shared knowledge false until
	      corrected.  If changes do occur, it is sometimes said
	      "the resource has moved", and appropriate notifications
	      and forwarding SHOULD be made.  The term "moved"
	      suggests that a URI is a location for a resource, and
	      this is a common metaphor, but it is only a metaphor.
	      Information changing over time can be handled without
	      changing RIF through various techniques such as having
	      the resource itself be a function mapping the current
	      time to a resulting value.

3.  URI-Scheme Languages  
	      
   In addition to serving as an argument for the RIF function and
   thereby identifying a resource, each URI MAY contain encoded
   (serialized) information.  The syntax and semantics of the encoding
   language are determined by the normative specificiation registed
   with IANA for the scheme name and MUST be subordinate to the syntax
   and semantics given in this document.

              a.  Scheme languages SHOULD be declarative in nature,
	      with the URI text conveying knowledge either directly or
	      indirectly about the identified resource.  An example of
	      a direct assertion is the "data" scheme, where the URI
	      text fully describes the identified resource.  An
	      example of an indirect assertion is the "http" scheme,
	      where the URI text conveys the network address of a
	      server which can communicate on behalf of or about the
	      resource.

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

That's it.  IMHO it nicely refactors some tricky issues, but I surely
can't claim to understand them all.  Probably the biggest thing is
pulling RIF out of the intrinsic nature of URIs and being explicit
about it.   Also I think it's important to be clear that using a URI
as a an argument to RIF is almost totally different from decoding it
according to some scheme-specific language.

      -- sandro
Received on Wednesday, 23 April 2003 16:31:45 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Thursday, 13 January 2011 12:15:31 GMT