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Re: separating consistency, conformance from the state of the web

From: Jeff Heflin <heflin@cse.lehigh.edu>
Date: Tue, 03 Jun 2003 10:15:24 -0400
Message-ID: <3EDCAD7C.FB4284C3@cse.lehigh.edu>
To: Dan Connolly <connolly@w3.org>
CC: www-webont-wg@w3.org

Dan,

I agree that the semantics should abstract out the treatment of
retrieving things from the Web. Note that the semantics for the abstract
syntax treats imports differently than what you read. I quote from
Section 3.4:

"Aside from this local meaning, an owl:imports annotation also imports
the contents of another OWL ontology into the current ontology. The
imported ontology is the one, if any, that has as name the argument of
the imports construct. (This treatment of imports is divorced from Web
issues. The       intended use of names for OWL ontologies is to make
the name be the location of the ontology on the Web, but this is outside
of this formal treatment.)"

The section goes on to say that an interpretation satisfies an ontology
iff it satisfies each ontology referenced by an imports annotation. I
think this section provides a clean and clear treatment of imports (good
work Peter!).

To align the RDF compatible semantics better, we could change the
imports closed definition in 5.3 from

"K is imports closed if for every triple in any element of K of the form
x owl:imports u then K contains the result of the RDF processing of the
RDF/XML document, if any, accessible at u into an RDF graph."

to:

"K is imports closed if for every triple in any element of K of the form
x owl:imports u then K contains the RDF graph identified by the URI u."

Now, I realize that there is a nit in this description because RDF
doesn't actually allow you to identify a graph with a URI, thus the
assumption is that the graph is identified by the URI of the document it
is in. I could live with this nit. Or we could raise an issue to RDF
Core...

You also say..

> i.e. deleting document X can cause document Y to cease
> to be an OWL DL document.

Of course! And if I deleted text from an OWL DL document, it may also
cease to be an OWL DL document. Why should it be any other way? Now we
could consider whether we should warn people that some people may not
play nice and might go changing their ontologies out from under you.
Personally, I think it is obvious and really more of material for OWL
books than OWL specs.

Jeff

Dan Connolly wrote:
> 
> Persuant to my action of 8May,
> 
> [[
> 3.2 use of xml:base
> ...
> new ACTION Dan - create a test for this
> ]]
> -- http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0120.html
> 
> I'm reviewing the specification of imports,
> entailment, consistency and such, and I think
> the imports nonsense has leaked into parts of the
> spec that we agreed not to let it leak into.
> Hmm... no, on review I see that the business about keeping
> imports closure separate from entailment never
> actually got decided by the WG. In any case...
> 
> My understanding of the design was: entailment (and
> hence consistency) was defined as a purely mathematical
> relationship between graphs, with no dependency on the state of
> the web.
> 
> Imports closure is a sort of scruffy notion involving
> web access.
> 
> You can do the scruffy imports closure stuff, take the
> resulting graphs, and test them for consistency,
> entailment, and all that. But the definition of
> entailment and consistency itself doesn't depend
> on the state of the web.
> 
> This is not the way the specs are written.
> 
> One particular problem is this ill-formed
> definite description in S&AS:
> 
> "the RDF/XML document, if any, accessible at u"
> http://www.w3.org/TR/2003/WD-owl-semantics-20030331/rdfs.html#RDF_graph_imports_closure
> 
> In the general case, there's more than one RDF/XML document
> accessible at u.
> 
> That's in the definition of imports closure; I expect
> a certain amount of scruffiness there. But the following
> definions (from section 4.1. Document Conformance of
> the test doc) all depend on it:
>   - OWL DL document
>   - OWL Lite document
>   - consistent OWL Lite/DL document
>   - consistent OWL Full document
> 
> i.e. deleting document X can cause document Y to cease
> to be an OWL DL document.
> 
> Also, I think there's a sort error in section 4.1.2. Semantic
> Conformance of test: "An OWL Lite or OWL DL document D
> is consistent ... if and only if ... such that I
> satisfies an abstract ontology O equivalent to D".
> D is a document but equivalence is defined over graphs.
> 
> I'd rather define conformance independent of the state of the
> web; here's an attempt:
> 
>   An OWL Full document set is a finite set of RDF/XML documents.
> 
>   An OWL Full document set is imports-closed if the corresponding
>   set of RDF graphs is imports closed [cf S&AS 5.3].
> 
>   An _OWL DL document set_ is an OWL Full document set
>   the merge of whose RDF graphs is an OWL DL ontology in RDF graph form.
> 
>   An _OWL Lite document set_ is an OWL Full document set
>   the merge of whose RDF graphs is an OWL DL ontology in RDF graph form.
> 
>   An OWL Lite or OWL DL document set consistent with respect to
>   a datatype theory T if and only if there is some abstract OWL
>   interpretation I with respect to T such that
>   I satisfies an abstract ontology O equivalent to D,
>   in which O has a separated vocabulary; and D is the merge
>   of the RDF graphs of the document set.
> 
>   An OWL Full document set is consistent with respect to
>   a datatype theory T, if and only if there is some OWL Full
>   interpretation I with respect to T such that I satisfies
>   all the RDF graphs corresponding to the documents in the set.
> 
> Note that consistency is defined independently of
> imports closed-ness.
> 
> In fact, since imports closure isn't really formally defined,
> I'd prefer to move it out of S&AS altogether. I'm pretty
> sure it's not needed there. I'd be happy to see it
> moved to the document conformance section of test.
> 
> --
> Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Tuesday, 3 June 2003 10:15:38 GMT

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