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Architecture Document: Terminology: Dereferencable, Retrivable, R esolvable.

From: Williams, Stuart <skw@hplb.hpl.hp.com>
Date: Fri, 12 Jul 2002 15:58:50 +0100
Message-ID: <5E13A1874524D411A876006008CD059F04A06F34@0-mail-1.hpl.hp.com>
To: "'www-tag@w3.org'" <www-tag@w3.org>

The retentive in me is coming out...

In writing about the things folks might do with URI (and URI references) we
speak variously of resolvable, dereferencable and retrievable URI. However
it's not clear to me whether or not we have consistent notions the different
shades of gray that might be associated with these terms. If there are good
pre-existing definitions for these notions a pointer would be welcome.

For instance, a TAG finding might say that "All important resources should
be identified using deferencable URI" (for example). One might take that to
mean that a representation of the resource should be 'retrievable' using the
relevant URI (that's what it says at [1]). But I think one could also argue
that any of HTTP PUT, POST, HEAD or DELETE involve "deferencing" the URI. In
programming languages we apply the notion of dereference wrt to an object
reference or a pointer regardless of whether it is used on the left or right
hand side of an assignment. So... whilst to be 'retrievable' a URI must also
be 'deferencable' the act of 'derefencing' a URI does not necessarily imply
a safe 'retrival' operation. Likewise, to be 'dereferencable' a URI must
also be 'resolvable', the act of 'resolving' a URI being a pre-cursor to and
possibly entailed within the process of dereferencing a URI.

Does this make any sense or do such fine grain differences not matter in our
architectural writings?

Anyway, some proto defintions to chew on:

URI Resolution: 
  The process of determining the access mechanism and 
  appropriate parameters necessary to dereference a 
  URI. e.g. in the case of an HTTP URI, this process 
  resolves the URI into an IP address, a port number, 
  a host name (possibly optional) and a request URI.

  Resolution may require several iterations.

URI Dereference: 
  The process of using the access mechanism and 
  parameters generated by URI resolution to create, 
  inspect or modify resource state.

URI Retrieval: 
  The use of URI dereference to retrieve 
  representations of resource state. 
  [On the Web Retrival is always safe].



Stuart Williams

[1] http://www.w3.org/2001/tag/2002/0701-intro.html#dereference
Received on Friday, 12 July 2002 10:58:56 UTC

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