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Re: LANG: need to CLOSE Issue 5.6 Imports as magic syntax

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Wed, 30 Oct 2002 18:39:35 -0500 (EST)
Message-Id: <20021030.183935.107993234.pfps@research.bell-labs.com>
To: heflin@cse.lehigh.edu
Cc: www-webont-wg@w3.org

From: Jeff Heflin <heflin@cse.lehigh.edu>
Subject: Re: LANG: need to CLOSE Issue 5.6 Imports as magic syntax
Date: Wed, 30 Oct 2002 18:05:32 -0500

> Hi Peter,
> 
> Thanks for the suggestion. I have some comments below:
> 
> "Peter F. Patel-Schneider" wrote:
> > 
> > 
> > I endorse Jeff's proposal, with the following changes.  I'll start out with
> > the abstract syntax, as it is much easier to see what is going on here:
> > 
> > 1/ OWL abstract syntax ontologies can include Imports(<URI>) directives.
> > 
> > 2/ The closure of an OWL abstract syntax ontology is obtained by taking its
> >    directives and replacing any Imports directives by the directives of the
> >    OWL ontology found at the URI that is the argument of the Imports
> >    directives, unless the URI has already been so used in which case the
> >    Imports directive is simply removed.  This is done until there are no
> >    Imports directives remaining.
> 
> Since your definition explicitly includes "OWL ontology found at the URI
> that is the argument," we have to be explicit about the meaning of a URI
> that cannot be dereferenced. What would you suggest here?  I'm hesitant
> to simply say such expressions are meaningless. For example, it seems
> dangerous to say that if I commit to an ontology, but its server goes
> down, anybody is free to assume that there are no addtional consequences
> of my statements, even though there may be vital contract conditions or
> privacy information, etc. contained within the unavailable ontology.

My suggestion would be to change to 

 2/ The closure of an OWL abstract syntax ontology is obtained by taking its
    directives and replacing any Imports directives by the directives of 
    the OWL ontology, IF ANY,
    found at the URI that is the argument of the Imports
    directives, unless the URI has already been so used in which case the
    Imports directive is simply removed.  This is done until there are no
    Imports directives remaining.

This, I believe, neatly sidesteps the issue.  If dereferencing the URI (on
the LHS) gets a document, then all is well.  If dereferencing the URI does
not result in an error, then an application can do whatever it can do to
determine if the problem is permanent, in which case the application can
still proclaim completeness.  If an application cannot so determine, then
it can still proceed, but could not claim completeness.  

The situation is, of course, different on the RHS, but I do expect much
fewer Imports in conclusions.

> >    2a/ Other kinds of annotations are simply removed.
> 
> What do you mean by "other kinds of annotations" here?

I'm leaving the door open for other stuff, like version information.

> > 3/ An OWL intepretation of an OWL abstract syntax ontology is defined as an
> >    OWL interpretation of its closure.
> 
> Assuming we work the bugs out of 2, I could live with this (I still
> prefer soemthing strictly based on entailment).

Well this is as close as you are going to get, I think.  How else could you
do it?

> > 4/ An OWL ontology entails an OWL axiom if all interpretations of the
> >    ontology are OWL interpretations of the axiom.  One OWL ontology entails
> >    another if all interpretations of the first ontology are interpretations
> >    of the second.
> 
> Do we need this last bit here (one OWL ontology entails another)? It
> seems to be what leads to the problem in your example below.

Well, it is not completely necessary to have an ontology on the RHS, I guess.
The issue of syntax still arises.

> > Note that this does not *require* an OWL agent to actually construct the
> > closure to compute entailment.  The OWL agent could do whatever it wanted,
> > as long as the correct result was obtained.
> > 
> > I have a modification of the semantics document that incorporates these
> > (minor) changes to Imports for the abstract syntax and its direct semantics.
> > 
> > Unfortunately, there are problems when the RDF syntax is considered.
> > 
> > 1/ What is the syntax for imports (and other annotations)?
> > 
> > 2/ If the syntax results in n-triples, then these n-triples will interfere
> >    with entailment.
> > 
> >    For example, does the OWL ontology
> > 
> >    http://foo.ex/bar
> >         <http://foo.ex/bar#John> <http://foo.ex/bar#loves> <http://foo.ex/bar#Mary> .
> > 
> >    entail
> > 
> >    http://foo.ex/baz
> >         <http://foo.ex/baz#> [owl:imports] "http://foo.ex/bar" .
> > 
> >    This is why I suggested that imports be made an attribute of the enclosing
> >    rdf:rdf (or other) element.
> > 
> > peter

peter
Received on Wednesday, 30 October 2002 18:39:53 GMT

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