- From: <noah_mendelsohn@us.ibm.com>
- Date: Fri, 6 Oct 2006 23:05:27 -0400
- To: Patrick Stickler <patrick.stickler@nokia.com>
- Cc: "Dan Connolly" <connolly@w3.org>, "ext Booth, David (HP Software - Boston)" <dbooth@hp.com>, raman@google.com, "Williams, Stuart (HP Labs, Bristol)" <skw@hp.com>, www-tag@w3.org
Patrick Stickler writes:
> (b) if is known (by extra-web means) that a given URI denotes a
> representation, then the agent is licensed to expect that every time
> it dereferences that URI it will get the same exact byte sequence
Yes, if you really mean "that" representation, but I think we're glossing
over an ambiguity.
Consider one of my favorite examples, which is a clock resource. The
clock updates in real time, and representations of it change accordingly.
For this example, assume that the clock resource at
http://example.org/clock supports content negotiation. It returns the
representation of the clock as your choice of text/plain, in which case
you get back the date and time as text, or image/jpeg, in which case you
get the image of a round analog clock showing the current time.
Your analysis seems to apply to the case where we want a URI for the
particular resource returned at, say 3PM, and I think your analysis is
coherent for that case. I don't think it's the main case of interest.
What I think we're mostly considering is more along the lines of two
additional resources which might be named:
http://example.org/clock?rep=text
http://example.org/clock?rep=image
These would not in fact return the same representation on successive
accesses, but would invariably return representations using the particular
media types. I also think this is an appropriate use of URIs for
representations. So, I don't think that in all useful cases "URI denotes
representation" implies "denoted representation octet stream is
invariant". I think the two URIs above denote representations of the
original clock resource if the authority at example.org says they do.
Also, I think I'm right that the term "representation" is appropriately
applied not just to the octet sequence returned, but to some of the
associated control data such as Content-type that's typically carried in
some of the returned HTTP headers.
Noah
--------------------------------------
Noah Mendelsohn
IBM Corporation
One Rogers Street
Cambridge, MA 02142
1-617-693-4036
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Received on Saturday, 7 October 2006 03:05:39 UTC