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Use cases from Jonathan

From: Booth, David (HP Software - Boston) <dbooth@hp.com>
Date: Tue, 29 Apr 2008 05:11:39 +0000
To: Jonathan Rees <jar@creativecommons.org>
CC: "public-awwsw@w3.org" <public-awwsw@w3.org>
Message-ID: <184112FE564ADF4F8F9C3FA01AE50009FCF22AD693@G1W0486.americas.hpqcorp.net>

> From: Jonathan Rees [mailto:jar@creativecommons.org]
> [ . . . ]
> Here are some of the cases I'm thinking of:

I'll first just answer these in prose, since I can do that more quickly than in N3.  I'll be using ftrr:IR definition of "information resource" at

> 1. I have two URIs X and Y. By varying Accept-Language I learn that I
> can retrieve French and Spanish variants of something via URI X, and
> Spanish and German variants of something via URI Y. The Spanish
> variants retrieved via X and Y are the same. All responses are 200s.
>         - Is it possible that X and Y denote the same thing?

Yes, X and Y can denote the exact same ftrr:IR.  Bear in mind that one of the parameters to an ftrr:IR function is the request, and the request includes the URI of the resource whose representation is being requested, hence there is no way to use deferencing alone to reliably establish that two URIs denote different ftrr:IRs.   This reflects the actual capabilities of Web servers.

>         - Is it possible that X and Y do *not* denote the same thing?
>             (assuming that responses are known to be time invariant.)

Yes.  Since the set of <Time, Request, Representation> tuples that make up a ftrr:IR can be infinite, dereferencing two URIs cannot definitively establish that they denote the same ftrr:IR.  They could denote ftrr:IRs that differ in <Time, Request, Representation> tuples that your dereferencing did not test.

>         - Is it necessary that X and Y do not denote the same thing?

No, as explained above.

> 2. Suppose that the values I retrieve (in different languages, say)
> via a URI X say contradictory things - for example, one says that
> Rome is the capital of Italy, and another says that Paris is the
> capital of Italy.
>         - Does X denote an information resource, given that the values
> cannot both be representations of the same information?

Yes, X still denotes an ftrr:IR, even though it apparently violated the AWWW principle that each language-specific representation carries the same abstract information.  Bear in mind that on the Web, anyone can say anything about anything, including making statements that are false.  In this case, the abstract information that was carried was the assertion that both Paris and Rome are the capital of Italy.  The assertion happens to be false, but its falsity does not change the fact that X denotes an ftrr:IR.

>         - If so, does it denote a "bad" information resource?

I'm not sure what you mean by bad.  The ftrr:IR is perfectly fine as an ftrr:IR, but it happens to convey false information.

>         - If not, what does it denote, if anything?
>         - Assume unchanging whatever if necessary in order to
> make these questions nontrivial.
> 3. Suppose I set up a web server responding to requests for some URI
> X as follows:
>         - A URI for an IR on the web is chosen at random and
> a value is fetched using that URI

Let's call this second URI Z, and assume Z != X.

>         - The value is returned as the payload of a 200 response

Okay, so when X is dereferenced, a representation from Z is returned in a 200 response, right?

> Questions:
>         - Does X denote an information resource?

Yes.  The dereference of X resulted in a 200 response, therefore X denotes an ftrr:IR.

>         - If so, what information do its referent's
> representations represent?

A random representation chosen from the Web.

It sounds like you may be trying to view multiple representations as (perhaps lossy) encodings of some abstract information.  That view only applies to content negotiation, which is only *one* possible use of the Request parameter of an ftrr:IR function:

  f: Time x Request --> Representation

>         - If not, what could X's referent be, if it has one?
> Is it a "bad" information resource, or something else?

There is nothing wrong with it as an ftrr:IR, but whether you find it useful is up to you.

>         - Is the web site behaving within the limits
> specified by RFC2616 and/or AWWW?

Yes, provided we assume that AWWW adopts the ftrr:IR definition of "information resource".

> All these questions can be expressed in RDF. I can come up with more
> cases like this, if you like, but I think you get the idea so let's
> start with these.

Let me know if you still want N3 answers to these.

David Booth, Ph.D.
HP Software
+1 617 629 8881 office  |  dbooth@hp.com

Opinions expressed herein are those of the author and do not represent the official views of HP unless explicitly stated otherwise.
Received on Tuesday, 29 April 2008 05:13:27 UTC

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