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RE: ISSUE-65 (excess vocab): REPORTED: excessive duplication of vocabulary

From: Boris Motik <boris.motik@comlab.ox.ac.uk>
Date: Wed, 21 Nov 2007 09:31:49 -0000
To: "'OWL Working Group WG'" <public-owl-wg@w3.org>
Message-ID: <001101c82c21$57630830$2711a8c0@wolf>


I do agree that duplication of vocabulary is rather nasty. I've spoken to Jim Hendler at ISWC about it, and we came to a possible
solution, which I'd like to overview next. Before giving the solution, however, let me just recapitulate why we introduced the
duplicated vocabulary in the first place.

1. OWL 1.1 allows the same URI to be used as both an object and as a data property. (OWL 1.1 in general allows for punning; however,
for this particular problem, only punning on object and data properties is a problem. Thus, let us not discuss here the general
problems of punning in OWL 1.1 - this should be discussed separately.)

2. Parsing OWL RDF is difficult: one needs to first scan the file for the appropriate rdf:type triples, after which one needs a
second pass to actually output the axioms. Assuming that you parse just one ontology, this is a pain but not a serious problem;
however, ontology imports exacerbate this problem. Assume that you are parsing an ontology O that imports an ontology O'.
Furthermore, let us assume that O contains, for example, a someValuesFrom restriction on the property p. In OWL 1.0 it can happen
that the triples in O do not allow us to disambiguate the type of p; thus, we need to look at the imported ontology O' to find out
what the correct type of p is. This makes parsing of OWL RDF really difficult: you can't process an ontology by itself, but you need
to look at the imported ontologies as well.

Even worse, what if the imported ontology O' is not in OWL RDF but in some other format? (For example, KAON2 allows a file ontology
to import an ontology that resides in a relational database.) Parsing is now next to impossible. Thus, to allow parsing an ontology
O by looking only at the triples in O, we introduced the typed vocabulary.


And now for the solution.

I do agree that the first point is not really a use-case: I do not expect that users will actually want to use the same URI as both
an object and a data property. In contrast, being able to parse each ontology by itself seems like a desirable property that should
be preserved. Hence, I propose to change the specs as follows:

1. I would leave the structural specification as it is. In this spec, I would allow the same URI to be used as both an object and a
data property, and I would leave the typed vocabulary as it is. This is not so much driven by the desire for punning; rather, the
structural specification is intended to provide guidance for implementors of OWL APIs. In all APIs I know of, you do have a
separation of object and data properties; therefore, we should keep this separation in the spec as well. Whether you then allow the
same URI to be used as an object and as a data property is then really irrelevant for all intents and purposes.

2. A transformation of an ontology from the structural format (i.e., from the functional-style syntax) into RDF should be possible
only if you strictly separate the properties into object and data ones.

3. The transformation into RDF would then be roughly the same as in OWL 1.0, with the following difference: the resulting RDF graph
would be *required* to type all properties used in the graph.

4. An RDF graph G could be parsed into the structural format only if each URI that is used as a property is correctly typed IN THIS
GRAPH. If, for example, some URI p is used in a someValuesFrom restriction but G contains neither <p rdf:type owl:ObjectProperty>
nor <p rdf:type owl:DatatypeProperty>, then G would not constitute a valid OWL 1.1 DL ontology.

This solution seems to have the benefit of satisfying everyone: we can parse each RDF graph by itself, there is no typed vocabulary,
and most reasonable use cases seem to be satisfied. Let me know how you feel about this solution.



> -----Original Message-----
> From: public-owl-wg-request@w3.org [mailto:public-owl-wg-request@w3.org] On Behalf Of OWL Working
> Group Issue Tracker
> Sent: 20 November 2007 14:49
> To: public-owl-wg@w3.org
> Subject: ISSUE-65 (excess vocab): REPORTED: excessive duplication of vocabulary
> ISSUE-65 (excess vocab): REPORTED: excessive duplication of vocabulary
> http://www.w3.org/2007/OWL/tracker/issues/
> Raised by: Jeremy Carroll
> On product:
> The member submission documents seem to replace a good many properties from OWL 1.0 with three
> properties in OWL 1.1. (The old version, and two new versions, one for data properties, and one for
> object properties)
> This:
> - creates additional work for implementors
> - creates additional work for documentation writers
> - potentially creates confusion for people as they learn the language
> Do the benefits outweight these (and other) costs?
Received on Wednesday, 21 November 2007 09:32:37 UTC

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