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Re: URIQA

From: Patrick Stickler <patrick.stickler@nokia.com>
Date: Tue, 1 Jul 2003 11:56:19 +0300
Message-ID: <1057787352.IAA22192@phantom.w3.org>
To: "ext Paul Prescod" <paul@prescod.net>
Cc: <www-tag@w3.org>


----- Original Message -----
From: "ext Paul Prescod" <paul@prescod.net>
To: <Patrick.Stickler@nokia.com>
Cc: <www-tag@w3.org>
Sent: 30 June, 2003 13:45
Subject: URIQA


> This document:
>
> http://sw.nokia.com/URIQA.html
>
> says"
>
> "However, semantic web agents (at present at least) are not able to deal
> as well with the broad range of possible representations which might be
> associated with a resource; and in nearly all cases, are unnable to make
> any use of such representations, as they are  typically intended for
> human rather than machine consumption. Semantic web agents, not being
> any where near as intelligent as most humans, require  information which
> is explicit and formally defined. In short, semantic web agents need
> concise, bounded descriptions of resources, rather than arbitrary
> representations of them.
>
> Concise bounded descriptions of resources can be considered to be a form
> of representation, however they are a highly specialized form and not
> the most usual or obvious form in a web primarily intended for human
> consumption. They are, however, the key form of representation which
> semantic web agents need in order to reason about such resources and
> adjust their behavior accordingly."
>
> Then you go on to add some headers to HTTP etc. Why not merely have the
> agents ask for representations they can deal with using conneg. If the
> representations are available, they are good to go. Otherwise they are
> out of luck.

This works for GET, but not for PUT or DELETE.

An early stage of URIQA development actually defined special MIME types
for concise bounded descriptions (in an attempt to try to accomplish what
was
needed without any extensions to the present Web architecture) -- but
ambiguity
arises when performing e.g. a PUT because the behavior of the server differs
depending on whether the input is a representation or description. If it is
a
representation, the server completely replaces any existing representation
with the input. Whereas, if the input is a description, the SW enabled
server
will augment the total body of knowledge known about the resource with
the additional knowledge provided as input.

Likewise, a DELETE request with an input description does not delete
all knowledge known about a resource, but only that which is specified
in the request input.

So simply specifying the MIME type of the input cannot capture all the
needed semantics.

To do this, the best solution that I've been able to come up with which
requires the least modification to the existing Web architecture is a single
header (serving as a flag) which allows us to differentiate between dealing
with representations from dealing with descriptions.

It is essential that we do differentiate between dealing with descriptions
versus representations because of the difference in behavior needed
with PUT and DELETE with regards to complete replacement/deletion
of a particular representation of a resource versus update
(addition/deletion)
of knowledge maintained by the server about a given resource.

> I think that the semantic resources should also have their
> own separate URIs for when you wish to unambiguously address into them.

I agree, and if you look at the behavior of the reference implementation of
URIQA (and this is also noted in the URIQA spec) all concise bounded
descriptions are distinct resources in their own right, and are given
distinct
URIs.

This also allows one to use PUT/DELETE to interact with those distinct
representations, including the use of conneg, in a traditional fashion.

Cheers,

Patrick


>   Paul Prescod
>
>
Received on Tuesday, 1 July 2003 04:56:31 UTC

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