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Re: rev and the costs of inverses/aliases in SPARQL

From: Dan Connolly <connolly@w3.org>
Date: Mon, 08 Mar 2010 11:36:52 -0600
To: Bijan Parsia <bparsia@cs.man.ac.uk>
Cc: public-sparql-dev <public-sparql-dev@w3.org>, public-rdfa <public-rdfa@w3.org>
Message-ID: <1268069812.3952.6007.camel@pav.lan>
On Mon, 2010-03-08 at 16:16 +0000, Bijan Parsia wrote:
> On 8 Mar 2010, at 15:00, Dan Connolly wrote:
> 
> > I just ran into this message again from an HTML 5 validator:
> >
> > "The rev attribute on the a element is obsolete. Use the rel attribute
> > instead, with a term having the opposite meaning."
> 
> Note that this is the OWL 1 situation (i.e., must coin a name to have  
> an inverse).

Ah... I forgot about that.

>  OWL2 has an operator as do most DLs directly.
> 
> just having fought with an RDFa example:
> 
> <a  about='owl:Class' rev="rdf:type" href='http://www.pizzas- 
> online.org/pizza-ontology.owl#rosa'>
> 	<span property='rdfs:label'>Momma's Special Pizza</span>
> </a>
> 
> I did find the rev confusing (I was starting from someone else's;  
> href's behavior is annoying in this case).
> 
> [snip]
> > Doesn't that just gum up the works when doing SPARQL queries? Which
> > do you query for, abridgement or abridgementOf? Or do you use
> > a UNION?
> 
> Or add the requisite rule/owl axiom.

Would you elaborate on that, please?
(a) do any/many/most widely-used SPARQL engines support adding
OWL axioms this way?
(b) what are the costs of this approach in time/space?

One project I worked on used forward chaining in virtuoso, so
it increased the storage costs (doubled the storage for statements
with properties that have inverses)... I'm not sure about the
impact on query run time, but it took a few hours to do the
pre-query forward chaining. I think our KB had a few million
statements in it.


> [snip]
> > Would the RDFa authoring community miss a/@rev if it went away?
> > Does anyone have 1st-hand experience to share?
> 
> I would miss the inverse operator in OWL (esp. in class expressions).  
> Dunno if I'd miss rev.
> 
> One thing that seems to be the case in my brief foray is that being  
> too clever is bad and will bite you hard. The above example is too  
> clever. I should have done something like:
> 
> <a href='http://www.pizzas-online.org/pizza-ontology.owl#rosa'>
> 	<span rel="rdf:type" resource="owl:Class"/>
> 	<span property='rdfs:label'>Momma's Special Pizza</span>
> </a>
> 
> So, at least from this example, not only would I not miss rev, but I  
> would have avoiding going down a wrong path.
> 
> Cheers,
> Bijan.
> 
> 


-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
gpg D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E
Received on Monday, 8 March 2010 17:36:55 GMT

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