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RE: statements about resources vs. representations

From: Booth, David (HP Software - Boston) <dbooth@hp.com>
Date: Sat, 22 Nov 2008 01:27:14 +0000
To: "noah_mendelsohn@us.ibm.com" <noah_mendelsohn@us.ibm.com>, Pat Hayes <phayes@ihmc.us>
CC: Alan Ruttenberg <alanruttenberg@gmail.com>, Harry Halpin <hhalpin@ibiblio.org>, Jonathan Rees <jar@creativecommons.org>, "public-awwsw@w3.org" <public-awwsw@w3.org>
Message-ID: <CD2B872281385A439B98164F5351E6DD39C3A9B14C@GVW1144EXB.americas.hpqcorp.net>

Noah,

If one accepts the idea that an InformationResource is essentially a function from (Time x Request) to Representation, then I think the distinction that you are making is very clear and simple: it is the difference between x as a Representation and y as a <Time, Request, Representation> tuple.


David Booth, Ph.D.
HP Software
+1 617 629 8881 office  |  dbooth@hp.com
http://www.hp.com/go/software

Statements made herein represent the views of the author and do not necessarily represent the official views of HP unless explicitly so stated.


> -----Original Message-----
> From: public-awwsw-request@w3.org
> [mailto:public-awwsw-request@w3.org] On Behalf Of
> noah_mendelsohn@us.ibm.com
> Sent: Friday, November 21, 2008 8:07 PM
> To: Pat Hayes
> Cc: Alan Ruttenberg; Harry Halpin; Jonathan Rees; public-awwsw@w3.org
> Subject: Re: statements about resources vs. representations
>
>
> Reflecting on the note I sent below, I realize that there's a
> subtlety I
> didn't deal with.   There are at least two abstractions we
> might want to
> identify:
>
> 1) A representation in the sense of a particular set of bits sent at a
> particular time from an HTTP resource to a client or proxy,
> or conversely,
> such a representation sent upstream with PUT or POST.  By
> this definition,
> any representation involved in a subsequent interaction would
> necssarily
> be a different one.
>
> 2) A representation defined to be the information sent with a
> GET, PUT,
> POST, etc.  By this definition, it's at least possible that
> the same URI
> would be used to identify the representation that resulted
> from, say, two
> or more GETs.  I believe the natural way to go down this path
> is to allow
> the same URI to be used to identify representations with the
> same content,
> even if provided as representations from very different
> resources.  For
> example, the representation that is Content-type: text/plain
> with entity
> body "hello world" could have the same URI even if returned on GETs to
> many different resources.
>
> When I claimed that I wanted to indicate that a given
> representation was
> poorly formed, I could have meant in the sense of (1) or (2).
>  If I want
> to make a statement that a particular representation was
> received at 4PM,
> I probably mean in sense (2).  Or maybe for that case I need
> a URI for the
> HTTP response, which contains a representation but
> potentially contains
> additional information as well.
>
> Anyway, I realized that there is potentially such an ambiguity, and I
> think we should be very clear which of the possible
> abstractions we refer
> to when we decide to identify a "representation" with a URI.
>
> Noah
>
> --------------------------------------
> Noah Mendelsohn
> IBM Corporation
> One Rogers Street
> Cambridge, MA 02142
> 1-617-693-4036
> --------------------------------------
>
>
>
>
>
>
>
>
> Noah Mendelsohn
> 11/21/2008 06:22 PM
>
>         To:     Pat Hayes <phayes@ihmc.us>
>         cc:     Alan Ruttenberg <alanruttenberg@gmail.com>,
> Harry Halpin
> <hhalpin@ibiblio.org>, Jonathan Rees <jar@creativecommons.org>,
> "public-awwsw@w3.org" <public-awwsw@w3.org>
>         Subject:        Re: statements about resources vs.
> representations
>
>
> Pat Hayes writes:
>
> > I think what Harry should have said is that they are too
> > ephemeral for someone to want to give them an enduring name or
> > identifier. But there are other ways to refer to things than
> > baptizing them with a URI for all time.
>
> On this I don't think I agree.  We're talking about the Web here, and
> what's more, I think a representation is an information
> resource.  I mean,
>
> not only can the thing be represented as a computer message, the whole
> point of it is to be sent in a computer message!  The key
> architectural
> imperative for the Web is "Identify with URIs."  I see no
> reason why, in
> cases where you do want some means of identifying a particular
> representation, a URI wouldn't be the way to do it.  When I make that
> choice, I get a variety of advantages:  I can make Semantic
> Web statements
>
> about the representation (it was buggy, it took a long time
> to arrive, it
> was cached at proxy p1, etc.) in the natural way without resorting to
> indirection;  I think I could even choose to run a server that would
> respond to GETs with representations of, well, the representation.  I
> think the usual rules of the Web apply well here:  when you need to
> identify something, do it with URIs.
>
> Noah
>
> [1] http://www.w3.org/TR/webarch/#pr-use-uris
>
> --------------------------------------
> Noah Mendelsohn
> IBM Corporation
> One Rogers Street
> Cambridge, MA 02142
> 1-617-693-4036
> --------------------------------------
>
>
>
>
>
>
>
>
Received on Saturday, 22 November 2008 01:29:30 GMT

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