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Re: MT for imports (was: Re: Imports Proposal)

From: Dan Connolly <connolly@w3.org>
Date: 07 Nov 2002 20:28:56 -0600
To: Pat Hayes <phayes@ai.uwf.edu>
Cc: Jeff Heflin <heflin@cse.lehigh.edu>, www-webont-wg@w3.org
Message-Id: <1036722536.11401.10904.camel@dirk>

On Thu, 2002-11-07 at 18:01, pat hayes wrote:
[...]
> Sorry it gets a bit 
> complicated, but it really is an indexical, and indexicals are rather 
> complicated to talk about.

Yes, I agree something like this is necessary to formally
specify imports. Hence my hesitation to attack it
in this version.

But I haven't convinced the rest of the group that
we can advance the state of the art without it,
so... whee! here we go...


> -----------
> Long version.
> 
> The truth conditions for owl:imports are non-standard in two ways, 
> both of which require us to modify the semantics, but in ways that 
> are orthogonal to the other semantic issues, fortunately.
> 
> First, they are given for a particular token of owl:imports in a 
> particular document, and may be different for other tokens of the 
> same triple in other documents. This is actually not possible in a 
> conventional semantic theory, but we will tackle it directly by 
> altering the semantic rules. An interpretation is usually defined in 
> terms of a mapping from a vocabulary, ie a set of names. We will 
> instead consider this to be a mapping from a set of name *tokens*, 
> where we will say that for all tokens not in an imports triple, that 
> all tokens of a given name map to the same meaning. This reproduces 
> the usual semantics for the rest of the language but allows us to 
> distinguish one token of owl:imports from another. (To sum up, one 
> could say that the meaning of owl:imports is *essentially indexical* 
> (http://csli-publications.stanford.edu/site/1575862697.html) )
> 
> Second, they use urirefs to refer to documents, in ways that go 
> beyond the standard semantic rules for RDF but which have been argued 
> for by many eminent authorities. So let us follow those authorities 
> and say that any token of an absolute HTTP URI in an imports triple 
> must always be interpreted as denoting the document which would be 
> retrieved by using the HTTP protocol on the WWWeb,

Umm... 'the document... ' is an ill-formed definite
description; URIs don't uniquely determine documents; maybe
you treated that later... but it doesn't just vary on time; it
can also vary by user-agent, media types requested,
authentication credentials, etc.

> so that for 
> example I(http://www.coginst.uwf.edu/~phayes) is required to be a 
> certain document with a picture of an idiotic grin on it, in all 
> interpretations. This leaves open the issue of how to define 
> 'document', but we need not do that, since the only documents we need 
> to worry about are OWL documents that define an OWL/RDF graph; so we 
> will treat all such HTTP URIs as denoting an OWL/RDF graph, and if 
> there isn't any OWL in the document, or if you get a 404 error, then 
> that is the empty graph.
> 
> However, since the result of an HTTP operation depends on the state 
> of the WWWeb, the truth of any particular owl:imports token may vary 
> depending on the state of the web. Inferences made from any such 
> triple should therefore be considered to incorporate an implicit 
> reference to the state of the WWWeb at the time the inference was 
> made. Users SHOULD use some means to distinguish state-dependent 
> inferences from non-state-dependent inferences. Owl:imports is the 
> only item in the OWL namespace that requires this special treatment.

I thought you had a much nicer, cleaner design a while back... the
way I undestood your message of 9Oct
  http://lists.w3.org/Archives/Public/www-webont-wg/2002Oct/0057.html
was that an interpretation includes an "observation" of
the Web; i.e. this dependency on the state of the web
is treated just like other issues regarding the
connection between names and their denotation: we
suppose there might be various name<->denotation
connections in various interpretation; as long
as an inference works in all such cases, we
regard it as valid.

So in addition to IS, CEXT, and IEXT, we'd introduce
something like IW, a mapping from names to graphs...
er... you called the KBs in your 3-line specification:

------------
owl:imports BBB

is true in an interpretation I just when the owl KB gotten by 
dereferencing BBB is true in I, OR if there is no such owl KB.
-------------

That seems like a simpler way to deal with all this stuff...
is it incomplete in some essential way?

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Thursday, 7 November 2002 21:28:23 GMT

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