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RE: A proposal for ISSUE-104 (built-in vocabulary)

From: Boris Motik <boris.motik@comlab.ox.ac.uk>
Date: Thu, 12 Jun 2008 09:51:17 +0100
To: "'Michael Schneider'" <schneid@fzi.de>
Cc: <public-owl-wg@w3.org>
Message-ID: <002401c8cc69$7a90c700$4012a8c0@wolf>

Hello,

Thanks Michael for this really interesting example. This only reinforces my view that we should simply prohibit the usage of all
rdf:* and owl:* vocabulary in the data as it is messy and brittle. Even if we can solve this problem, I doubt that we would be able
to come up with a solution for which we can be reasonably sure that there are no errors.

Regards,

	Boris

> -----Original Message-----
> From: Michael Schneider [mailto:schneid@fzi.de]
> Sent: 12 June 2008 09:31
> To: Boris Motik
> Cc: public-owl-wg@w3.org
> Subject: RE: A proposal for ISSUE-104 (built-in vocabulary)
> 
> Boris Motik wrote:
> 
> >Hello,
> >
> >But consider the case where you use declare rdf:first as and
> >owl:ObjectProperty, but your ontology also contains a nominal
> >containing a literal. In the serialization of the ontology, you'll have
> >
> >_:x rdf:first "c"^^xsd:string
> >
> >but you'd also have
> >
> >rdf:first rdf:type owl:ObjectProperty.
> >
> >But then, you've just showed the constant "c"^^xsd:string into the
> >individual domain. Under OWL DL semantics, your graph is now
> >unsatisfiable.
> 
> I think, the actual problem is the reverse mapping. It would be necessary
> for the reverse mapping to clearly distinguish between syntax related usage
> (as in the "owl:oneOf(...)" expression), and custom usage (rdf:first as an
> object property in our example). Then, the resulting FS syntax would be
> something like:
> 
>   # mapping of the nominal containing a literal
>   ... OneOf( ... "c"^^xsd:string ... )
> 
>   # mapping of the custom usage of rdf:first
>   Declaration(ObjectProperty(rdf:first))
>   PropertyAssertion(rdf:first _:z ex:something)
> 
> So in this case, the URI 'rdf:first' would exclusively occur as an object
> property in the resulting FS ontology, and there would be no problem with
> the semantics.
> 
> However, I am not sure whether the current reverse mapping would provide
> this result. It might be (I would need to check) that, in the case that
> rdf:first is an allowed URI, the reverse mapping would see the isolated
> triple
> 
>   _:x rdf:first "c"^^xsd:string
> 
> and would try to map it into a data property assertion. This would be fatal,
> of course.
> 
> So the reverse mapping would perhaps need to be adjusted.
> 
> And now, I am not convinced anymore that it is perfectly possible to have a
> reverse mapping which always properly distinguishes between syntax and
> custom usage. For example, the same list expression in an RDF graph (or only
> a part of it) may be used both as part of the syntax and in a custom way:
> 
>     :alice rdf:type [
>         rdf:type owl:Class ;
>         owl:oneOf ( :person1 :person2 ) ]
> 
>     :alice :likes ( :person1 :person2 )
> 
> What to do here? The "canonical parsing process" in the current reverse
> mapping cannot simply remove the list after the first axiom has been mapped,
> since the list expression is still needed to process the second axiom. But
> when list expressions are /not/ removed after the mapping of syntax use,
> then I am not clear how to correctly cover the "punning-like" cases such as
> the one discussed above.
> 
> But even if it would turn out to be technically possible to always correctly
> distinguish between custom and syntax usage, adjusting the reverse mapping
> for handling custom use of RDF lists would perhaps significantly add to the
> complexity of the RDF mapping. The reverse mapping is currently already very
> complicated, and making it even more complex may lead to errors and other
> problems.
> 
> To make this clear: My original idea was to introduce custom usage of RDF
> lists (and reification, and ...), *if* we can get it mainly for *free*, by
> just not disallowing the respective URIs. But now, I see that the cost would
> probably be much higher than I expected.
> 
> So I won't push this topic any further, at least not for RDF lists (I did
> not yet consider RDF reification). This looks to me as something what
> /might/ be possible, but I rather tend to postpone this issue ("we currently
> don't know how to do this").
> 
> >Under OWL Full semantics, it is really not clear what happens.
> 
> The situation in OWL Full is much less complicated. :)
> 
> >Regards,
> >
> >	Boris
> 
> Best,
> Michael
> 
> >> -----Original Message-----
> >> From: Michael Schneider [mailto:schneid@fzi.de]
> >> Sent: 11 June 2008 18:16
> >> To: Boris Motik
> >> Cc: public-owl-wg@w3.org
> >> Subject: RE: A proposal for ISSUE-104 (built-in vocabulary)
> >>
> >> Hi Boris!
> >>
> >> Regarding the 'rdf:first' problem: Your proposal would introduce
> >special
> >> treatment for the List vocabulary in OWL 2. My own idea, stated in an
> >> earlier mail, was the opposite: To simply ignore the list vocabulary
> >(except
> >> in those parts of the reverse mapping where it is applied as part of
> >the
> >> syntax).
> >>
> >> This would have the effect that rdf:first would be just some URI. And
> >this
> >> would mean that, in order to use it, one would need to declare it to
> >be
> >> either an owl:ObjectProperty or an owl:DatatypeProperty, respectively.
> >For
> >> example, the following would then be legal OWL 2 DL:
> >>
> >>   rdf:List rdf:type owl:Class .
> >>   rdf:first rdf:type owl:DatatypeProperty .
> >>   rdf:rest rdf:type owl:ObjectProperty .
> >>   rdf:nil rdf:type owl:NamedIndividual .
> >>
> >>   :alice :likesNumbers ( 2 3 5 7 ) .
> >>
> >> The declarations could be imported, of course, no need to write them
> >down
> >> every time.
> >>
> >> It wouldn't be possible to use rdf:first both as an object and a data
> >> property in the same ontology. But this is what one would expect in
> >OWL 2
> >> DL.
> >>
> >> Michael
> >>
> >> >-----Original Message-----
> >> >From: public-owl-wg-request@w3.org [mailto:public-owl-wg-
> >request@w3.org]
> >> >On Behalf Of Boris Motik
> >> >Sent: Wednesday, June 11, 2008 12:33 PM
> >> >To: public-owl-wg@w3.org
> >> >Subject: A proposal for ISSUE-104 (built-in vocabulary)
> >> >
> >> >
> >> >Hello,
> >> >
> >> >The discussion around ISSUE-104 (reserved vocabulary) seemed to show
> >> >that lists and reification are the main, if not the only part
> >> >of the reserved vocabulary that might be useful in OWL 2 DL. (If we
> >feel
> >> >that it is necessary, we may verify this by sending an
> >> >e-mail to owl-dev once we have fleshed out our proposal. I personally
> >> >don't think we need to do this, given my experience how the
> >> >built-in vocabulary has been used in OWL 1.)
> >> >
> >> >Based on the assumption that we more or less agree on the above
> >> >observation, I would like to put forward a proposal for resolving
> >> >this issue. Before I do so, let me first explain why the obvious way
> >of
> >> >resolving the problem does not work.
> >> >
> >> >
> >> >1. A slight problem with exempting rdf:List from the reserved
> >vocabulary
> >> >---------------------------------------------------------------------
> >---
> >> >
> >> >For a property to be used in any OWL 2 DL axiom, the property must be
> >> >declared as either an object or a data property. Now this
> >> >causes a slight problem for rdf:List: we would make a hard-and-fast
> >> >choice about how to treat rdf:first. Thus, we would have to
> >> >decide whether rdf:first is an object or a data property, which would
> >> >essentially restrict the usage of lists in OWL 2 DL in a nasty
> >> >way.
> >> >
> >> >
> >> >2. A possible way forward
> >> >-------------------------
> >> >
> >> >To allow for lists, we would introduce four new vocabulary elements
> >in
> >> >OWL 2:
> >> >
> >> >- owl:List
> >> >- owl:firstLiteral
> >> >- owl:firstIndividual
> >> >- owl:rest
> >> >
> >> >To ensure semantic compatibility with OWL Full, we would make
> >owl:List a
> >> >subclass of rdf:List, owl:firstLiteral and
> >> >owl:firstIndividual a subproperty of rdf:first, and owl:rest a
> >> >subproperty of rdf:rest.
> >> >
> >> >We would extend the structural spec to provide built-in declarations
> >for
> >> >these properties (in the obvious way). We would also add a
> >> >subsection to the structural spec and to the primer about how these
> >are
> >> >to be used in ontologies.
> >> >
> >> >We would leave the rest of the built-in vocabulary in OWL 2 DL as it
> >> >currently is.
> >> >
> >> >Note that this does not address the reification vocabulary.
> >Reification
> >> >is considered bad in RDF anyway, and it would introduce
> >> >similar problems in OWL 2 DL; therefore, it seems to me that
> >disallowing
> >> >it in OWL 2 DL is not a big deal.
> >> >
> >> >
> >> >
> >> >Let me know how you feel about this.
> >> >
> >> >Regards,
> >> >
> >> >	Boris
> >> >
> >
Received on Thursday, 12 June 2008 08:52:52 GMT

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