Ryan Lee wrote:
> Chris Bizer wrote:
>
>> Hi Emmanuel,
>>
>> I think this is definitively useful behaviour. The question which is
>> coming
>> to my mind is, what should be the default behaviour?
>>
>> Should the query engine by default use subproperty and subclass
>> relationships, which I guess will slow it significantly down?
It will slow it down, but I'm not sure to what extent (this will
partially depend on the complexity of class and property hierarchies).
But I would say that the language's expressive power and ease of use is
more important than implementation/performance issues (though these of
course have to be taken into account).
>> My understanding is that Fresnel is about visualizing materialized RDF
>> graphs and inferencing (if needed) is done on a lower layer before
>> Fresnel
>> gets involved.
Yes indeed. But if you think about the Fresnel presentation designer, it
can be very convenient to write a single lens that will apply to a class
and all its subclasses. If you don't have subclass/subproperty
inferencing at the FSL level, you have to define as many lens domains as
there are subclasses. And the lens won't apply to subclasses that the
stylesheet designer did not know of (or forgot).
> This is the same approach SPARQL is also taking.
>>
>> Thus I think (if at all) you should tell the engine explicitly to do
>> inferencing using '!' and the none-inferencing case should be the
>> default.
>
>
> Agreed.
Ok, so we all seem to agree that this is a useful feature. We only
disagree on whether this should be the default behaviour and on the syntax.
I'm okay witht the idea of having the subclass/subproperty-unaware
version the default, but then I'm not sure I like "!" as the notation
for the subclass/subproperty-aware version. I can live with it, that's
mostly a question of personal taste, but if anybody has another idea for
how to convey this, please submit it. Unless everybody's happy with the
! notation, in which case we'll leave it as such.
>> -----Ursprüngliche Nachricht-----
>> Von: Emmanuel Pietriga [mailto:emmanuel.pietriga_at_inria.fr]
>> Gesendet: Donnerstag, 8. September 2005 12:21
>> An: Fresnel Dev
>> Betreff: FSL and subclass/subproperty relationships
>>
>> Hello all,
> Coming back to FSL, I've been wondering about the need/relevance of
> having an operator for ignoring subclass/subproperty relationships on
> node and arc location steps.
>
> The expression:
>
> */foaf:knows/foaf:Person
>
> selects all paths that:
> - have any resource as their first step,
> - traverse an arc labeled by the foaf:knows URI or any URI refering to a
> property declared as a subproperty of foaf:knows in an RDFS or OWL
> document,
> - end at a resource whose type is foaf:Person or one of its subclass.
>
> Now, there might be cases when one wants to select nodes which are
> instances of a specific class but not of its subclasses. Same thing for
> property arcs.
>
> I thought about introducing the bang operator to say this:
>
> */!foaf:knows/!foaf:Person
>
> would select all paths that:
> - have any resource as their first step,
> - traverse an arc labeled by the foaf:knows URI ONLY (arcs whose URI
> refers to a property declared as a subproperty of foaf:knows in an RDFS
> or OWL document would not be selected),
> - end at a resource whose type is foaf:Person ONLY (instances of
> subclasses would not be selected).
>
> Do we want this? If so, is '!' appropriate?
--
Emmanuel Pietriga
INRIA Futurs - Projet In Situ tel : +33 1 69 15 34 66
Bat 490, Université Paris-Sud fax : +33 1 69 15 65 86
91405 ORSAY Cedex FRANCE http://www.lri.fr/~pietriga
Received on Mon Sep 12 2005 - 07:37:15 EDT