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yet another resource/representation diagram

From: Jonathan Rees <jar@creativecommons.org>
Date: Fri, 6 Mar 2009 23:21:14 -0800
Message-Id: <52850DAB-99A1-4110-94CC-8BDB90451FBB@creativecommons.org>
To: AWWSW TF <public-awwsw@w3.org>
Cc: "Henry S. Thompson" <ht@inf.ed.ac.uk>
Inspired by some comments Henry made about conneg at the recent TAG  
meeting I've made a third diagram to attempt to fit the conflicting  
theories together; see [1].

This is a bit more focused than diagram #2 [2], and it no longer talks  
about URIs, just the things that might or might not be named.

The boxes are classes and the arrows are properties that might hold  
between members of the classes. 3D boxes are for things that have a  
time dimension of any kind.

The theories to be reconciled are:
   1. TimBL "generic resources" [3]
   2. REST [4]
   3. David Booth ftrr [5]
   4. HTTP [6]

I think the overall diagram makes a plausible story.
   - a single GR doesn't "know" (commit to, model) what  
representations are associated with its states
   - REST is very similar to David's ftrr - difference lies in  
treatment of request headers (e.g. User-agent)
   - a REST resource, or ftrr, commits at each time to some particular  
set of representations
   - thus there many REST resources that are all "faithful" to a  
single GR in the sense of delivering valid representations of the GR's  
states. Different granularity or identity criteria for the two classes.
   - GRs and REST resources are not inherently physically embodied
   - REST and ftrr are Platonic ideals (models) of hypothetical or  
real response sources
   - HTTP response sources are physically embodied, thus very  
different from both GRs and REST
   - but an HTTP response source can be "faithful" to a GR or a REST  
resource by implementing it correctly
   - an HTTP response source can do all sorts of things that are not  
modeled by GR or REST, such as deliver 3xx, 4xx, 5xx responses
   - RFC 2616 permits resources that are "network services" - it is  
not natural to talk about these having 'states' or 'representations' -  
not clear whether such services a REST resources at all - I don't  
think they should be considered so (service: random number generator,  
webcam, database query?)
  - not clear whether two distinct GRs can correspond to the same REST  
resource. I think not since then they would have incommunicable  
'essential characteristics'

Please don't jump on my terminology... it's easily changed. The main  
point is that the four theories are about different kinds of things  
with different identity criteria, but they can be related to one  
another in a sensible way.

I think it's important to understand this story well before attempting  
to answer any questions about "identification".

Jonathan

[1] http://www.w3.org/2001/tag/awwsw/jar-diagram-3.pdf
[2] http://esw.w3.org/topic/AwwswHome?action=AttachFile&do=get&target=URI-representation-resource-unified.pdf
[3] http://www.w3.org/DesignIssues/Generic.html
[4] http://www.ics.uci.edu/~fielding/pubs/webarch_icse2000.pdf
[5] http://www.w3.org/mid/184112FE564ADF4F8F9C3FA01AE50009FCF22AD676@G1W0486.americas.hpqcorp.net
[6] http://www.ietf.org/rfc/rfc2616.txt
Received on Saturday, 7 March 2009 07:21:55 GMT

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