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Re: ISSUE 5.6 - daml:imports as magic syntax

From: Dan Connolly <connolly@w3.org>
Date: 10 Sep 2002 11:22:22 -0500
To: Jeff Heflin <heflin@cse.lehigh.edu>
Cc: WebOnt <www-webont-wg@w3.org>
Message-Id: <1031674943.2992.1934.camel@dirk>

short version: please let's drop daml:imports altogether.

Elaboration:

I don't have any software that notices
whether daml:imports is there or not.
(well, it's treated like any other property,
but I have never built nor used any applications
that make use of that propoerty).
Hence, I almmost never put it in my data files.

Does anybody else have software that pays
any attention to daml:imports whatsoever?

Is daml:imports observable from a testing perspective?
Are there any conceivable daml:imports tests that
a piece of software could fail?


Regarding the issue Jeff discusses...

On Mon, 2002-09-09 at 16:23, Jeff Heflin wrote:
> 
> Problem: 
> --------
> If daml:imports is just another RDF or OWL property, then users can
> place restrictions, etc. on it. For example, consider a situation where
> there was a max cardinality of 1 on imports. If an ontology imported two
> or more ontologies, then this would effectively say that the ontologies
> are equivalent.

Yes, exactly.

> It is probably best to avoid such situations.

Well, if folks don't mean that, then they shouldn't say it.
But if they say it, why should we (i.e. implementors of OWL
softwre) not deduce that they meant it?


> Possible Solution:
> ------------------
> This seems to indicate that imports should be a "dark" property.

That seems like an awfully expensive solution. It seems
easier to put a "don't do anything silly" paragraph in the guide.


> Note
> that this isn't an issue in the Abstract Syntax, since in it, everything
> is essentially "dark." In Pat Hayes' recent OWL model theory, it should
> be sufficient to say that owl:imports is not an instance of owl:Object,
> owl:DatatypeValue, owl:Class, owl:ObjectProperty, or
> owl:DataTypeProperty.

That much I can live with, but...

> However, it would still be an rdfs:Property, but
> any RDF graph that uses it as a subject or object would not be
> well-formed OWL/RDF.

Why go that far? If they say owl:imports is an owl:ObjectProperty,
they've contradicted themselves. Too bad.

Why stop them from contradicting themselves in this way, though?

> Note, owl:imports doesn't fit into any of the
> classifications in the table in section 2 of the Hayes model theory, so
> perhaps a new classification called metaproperty or such is needed.

Poor choice of names.
'metaproperty' would make sense for something like cardinality;
i.e. a property about a property. But imports isn't a property
about a property.

> Semantics:
> ----------
> It is important that the semantics of owl:imports be added to any
> semantics documents.

Why? Could you please give the argument that this conclusion
comes from?

> To do this, we need to be able to refer to sets of
> OWL statements (such as a web page, a database with an OWL interface,
> etc.) This could probably be called a resource, but that term is also
> used to describe RDF instances, so for lack of a better term, I will
> choose the term graph for the time being. Let graph be a function from a
> URI (URL?) to an RDF/OWL graph. Each OWL graph has a set of entailments
> that are determined by the model theory. The semantics of a statement:
> 
> A owl:imports B.
> 
> are:
> 
> if graph(B) |= X then graph(A) |= X
> 
> (Note: Here, "|=" is the OWL entailment relation)
> 
> One question is whether we need something more specific in the model
> theory that, for example, uses ICEXT and IEXT.
> 
> Any comments or suggestions?
> 
> Jeff
-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Tuesday, 10 September 2002 12:22:22 GMT

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