W3C home > Mailing lists > Public > public-awwsw@w3.org > November 2008

Re: statements about resources vs. representations

From: Jonathan Rees <jar@creativecommons.org>
Date: Wed, 26 Nov 2008 08:49:13 -0500
Message-ID: <760bcb2a0811260549p79b5d1efp1f3eea00a96da5a7@mail.gmail.com>
To: "Booth, David (HP Software - Boston)" <dbooth@hp.com>
Cc: "Pat Hayes" <phayes@ihmc.us>, "public-awwsw@w3.org" <public-awwsw@w3.org>

On Tue, Nov 25, 2008 at 10:44 PM, Booth, David (HP Software - Boston)
<dbooth@hp.com> wrote:

> Okay, well, let's assume that "accessible" means that a representation is likely to be retrievable.

You have violated the cardinal rule of this group - define your terms,
either directly or by citation. You don't say what sense of
representation, or representation of what.

>... "if there exists an :InformationResource ir with a representation that was retrieved less than 24 hours ago, then ir is a :AccessibleIR".

define "with"

If :InformationResource is a new term we're defining, it can be
defined to be anything. But we already have a set of terms
(Accessible, AWWIR, repsentation-qua-AWWW, etc), and I want to see if
we can make reasonable stands or refinements regarding them and
relating them, based on what we think would be most helpful for
communication and for engineered artifacts.

>> httpRange-14 permits one to use http: URIs to name things that aren't
>> allowed by RFC 2616, but says that any 2xx-responder ought to be an
>> AWWWIR. However, incorrect use of the http: scheme so extended can
>> result in non-AWWWIRs that are 2xx-responders (e.g. Dublin Core URIs).
> I don't think that's quite the right perspective.  I think if a GET on a URI yields a 2xx response, that is conclusive evidence that the URI *does* denote an IR, regardless of anything else that the URI owner may state through other means.

I know you have urged people to believe this, but I do not see
evidence that any formal document licenses this statement. I know
others in the group, including me, expressly disagree, as IMO it
contradicts the "URI owner" section of AWWW, so please let's
just agree to disagree and try to move on.

> If the URI owner also declares through other means that the URI denotes Dan's car, then there is a URI collision:
> http://www.w3.org/TR/webarch/#URI-collision
> Another term for URI collision is "ambiguity", for example, when a single URI http://markbaker.ca/ denotes both Mark Baker the person and Mark Baker's web page.  As pointed out on slides 19-20 of
> http://dbooth.org/2008/irsw/slides.ppt
> this is architecturally identical to the problem that occurs when a URI for the protein AKT is minted, and AKT is later discovered to be three distinct proteins: AKT1, AKT2 and AKT3.  And as Pat Hayes has pointed out many times, this kind of ambiguity will never be eliminated.  Fortunately, such ambiguity is not a show stopper, because: (a) the ambiguity may not matter to many applications; and (b) when the ambiguity does matter, the ambiguous URI can be related to more specific URIs, using skos:narrower.

It is URIs that are ambiguous, not resources.  I can't say that one
person is skos:narrower than another.

If I read Pat and Harry correctly, ambiguity means that one
well-meaning agent can take a URI to denote one thing, and another can
take it to denote another, and this is, SOMETIMES, either unavoidable,
benign, or both.  (Still other agents may be formalists, and not care
what the name denotes at all, but only what inferences can be drawn
about them.) We can argue about that, but the main conclusion I draw
is that whenever binding of a URI to a thing (denotation) is in
question, you have to talk about who believes what - you have to
compare models.  Denotation is not objective.

Note that in a properly constructed ontology AKT would have a
definition as a class, and that definition would stick. If new
information contradicted old, that would either be the result of a
refutable statement about biology or a refutable statement about
curation (failure to respect a definition). Such situations are
unavoidable, but should motivate repair efforts (this is the doctrine
of "fallabilism").

>> But all that aside... one question I have is whether the classes
>> Edition and Accessible intersect.
> Strictly speaking, no.  But that won't stop people from using the same URI to denote both.  That's the ambiguity mentioned above.

OK, you and Tim and I now all agree that these classes - i.e. what RFC
2616 calls a "resource" (which we agreed seemed to be what Pat
considered the things that can be "accessed") and what AWWW calls an
"information resource" - are disjoint. That's HUGE progress!

Just because we don't know what kind of thing a URI denotes doesn't
mean that some future assertion (using the vocabulary we publish, say)
about it might not clear up the matter. If the classes are disjoint,
and someone uses the URI one day to mean a member of one class and one
day to mean a member of another, that is inconsistent (in the OWL
sense) and against AWWW (which says don't use one URI to name two
different things). The only way for someone to use a single URI to
make statements appropriate to both classes is if the classes

The ambiguity idea just says there may be multiple models that are all
OK. It doesn't mean it's OK to be inconsistent.

>  - an InformationResource is essentially a function from (Time x Request) to Representation; and

Not an objective statement. Do you mean "information resource" in the
AWWW sense? I don't see how you'd support that. If it's a matter of
definition, I wish you'd use a different term, like fftr:IR (which
would make this a definition).

>  - a URI denotes a resource through a two-step mapping from URI, to a set of assertions, to the resource, as described in
> http://dbooth.org/2008/irsw/slides.ppt

A set of assertions can constrain an interpretation (set of URI ->
resource bindings) to the extent that someone might say that they know
what the URI denotes (based on assuming the truth of the assertions).
But it cannot dictate it. Please don't use "denotes" as if it were an
objective fact - unless you are trying to define the term in a new way
- in which case it would be less confusing to say so, and define a new

I don't think we need to put words in the mouths of the authors of RFC
2616, AWWW, or the httpRange-14 resolution. I think it's OK to do a
modest amount of "we agree that what they probably meant was" stuff -
this should be limited consensus. I think it's OK to disagree, but
only if there is some grounds in bibliography or other parts of
reality for disagreeing - so that we can find out who's right. I think
it's OK to recycle terms used in they see documents as long as we're
always careful to say which definition is being used. I think it's OK
to make recommendations on how new terms are to be used, and maybe
even give recommendations on new ways to use a protocol such as HTTP.
But I'm going to cry foul if someone tries to commandeer the meaning
of a term, language, or protocol that's already defined and in use.

I'll continue to be a broken record for as long as you do. I hope we
can work out a common manner of speaking so that we can make progress

Received on Wednesday, 26 November 2008 13:49:53 UTC

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