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

From: pat hayes <phayes@ai.uwf.edu>
Date: Tue, 19 Nov 2002 19:01:38 -0500
Message-Id: <p05111b06ba007d2c14fd@[10.0.100.86]>
To: Dan Connolly <connolly@w3.org>
Cc: www-webont-wg@w3.org

>http://lists.w3.org/Archives/Public/www-webont-wg/2002Nov/0102.html

Dan,

I was getting back up to speed with webont and realized that I had 
missed that message.  Sorry I didn't get back to you about it before.

Anyway, I know its too late, but here's a reply.


>  > -----------
>>  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.

True, I should have made that clearer.

>  > 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?

We could express it that way, and then the HTTP protocol is a 
semantic restriction on IW, which is cute, indeed.

But I think this is really the same idea. It still needs to be 
relativized to tokens of URIrefs rather than the URIrefs themselves, 
if we want to be able to say 'AAA imports BBB' , i.e. not in AAA, as 
opposed to "I import BBB".  I hope that the WG didn't decide to allow 
one document to say that another document imports a third document. 
If we only allow self-importing then we don't need to be explicit 
about token/types and indexicality, and the IW idea will probably 
work fine, indeed.

Anyway. Sorry again that I missed responding to this earlier.

Pat



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Received on Tuesday, 19 November 2002 19:01:48 GMT

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