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Re: Returning to OWL and application profiles

From: Antoine Isaac <aisaac@few.vu.nl>
Date: Tue, 12 Oct 2010 19:59:24 +0200
Message-ID: <4CB4A1FC.4020000@few.vu.nl>
To: "Panzer,Michael" <panzerm@oclc.org>
CC: Mark van Assem <mark@cs.vu.nl>, Mikael Nilsson <mikael@nilsson.name>, public-lld <public-lld@w3.org>, "Young,Jeff (OR)" <jyoung@oclc.org>, Emmanuelle Bermes <manue.fig@gmail.com>
Hi Michael,

> this might be slightly off-topic, and I hope I am not beating a dead
> horse here, but I have major problems with talking about OWL as if it
> where a language allowing schema-like validation of data. It is not. I
> am not saying that this type of use cannot be achieved with OWL, but it
> is not trivial.
> Statements in OWL are interpreted as facts that are used to infer new
> pieces of knowledge. Axioms in OWL support that goal as they are treated
> as "inference rules," not necessarily as constraints aimed at triggering
> inconsistencies. A trivial example would be the following.

Well, your example is right, but this is just an example, and the first sentence of this paragraph is wrong: I can also exhibit OWL examples that are not meant at inferring new RDF facts but at checking the consistency of existing facts. The axioms about maximum cardinality, disjointness of classes, properties and individual are about that [1,2].

Granted, these axioms may fail at capturing all constraints you want to have in APs, and you may need some more close-world stuff like what Kendall is proposing. But that's another issue :-)



[1] http://www.w3.org/TR/2009/REC-owl2-primer-20091027/#Property_Cardinality_Restrictions
[2] http://www.w3.org/TR/2009/REC-owl2-primer-20091027/#Class_Disjointness

> My OWL AP says:
> "Every published book has at least one author and exactly one
> publisher."
> My data says:
> 1. "<MyBook>  is a published book."
> 2. "<MyBook>  was published by<Publisher1>."
> 3. "<MyBook>  was published by<Publisher2>."
> A possible reaction of a schema validation language would be:
> "This data is not compliant to the AP. You state that<MyBook>  is a
> published book, yet there is no author information, and it has two
> publishers! Your data is rejected because it is either bad or you lied
> about it."
> This would be the reaction of an OWL reasoner:
> "Thank you so much for this new information. I can now conclude that
> <Publisher1>  and<Publisher2>  refer to the same individual (no Unique
> Name Assumption, combined with a functional property) and that<MyBook>
> is connected to some individuals that are authors, but I don't know
> about them yet (Open World Assumption). I'll add the following facts to
> my knowledge base:
> 4.<Publisher1>  is the same as<Publisher2>.
> 5.<MyBook>  has some authors.
> Please visit again soon."
>> An alternative is to just accept OWL as a "syntax" for the AP
>> constraints, and implement your own checker on top of that. This
> removes
>> the need to develop your own language (and parser) which will contain
>> almost the same syntactical elements anyway.
> Again, I don't say it can't be done. As suggested by Mark, one viable
> approach would be to interpret OWL axioms with integrity constraint
> semantics. You wouldn't have to implement your own checker, however.
> Pellet ICV {1] sounds really promising in that regard, as it generates
> SPARQL ASK queries to validate your RDF against OWL axioms.
> SPIN [2,3] sounds like something similar to be explored as well.
>> From a slightly different perspective, I think RIF [4] is what could
> fill the gap in a more conformant way. RIF has a defined path to OWL and
> is an integral part of the Semantic Web stack, but I haven't figured out
> how to use it efficiently yet (I have had little exposure to rules
> languages in the past, so I need more time to get up to speed there.)
> Cheers
> Michael
> [1] http://clarkparsia.com/pellet/icv/
> [2]
> http://www.proxml.be/users/paul/weblog/aaad2/Integrity_constraints_in_SK
> OS_part_1_.html
> [3] http://www.spinrdf.org/
> [4] www.w3.org/2005/rules/
Received on Tuesday, 12 October 2010 18:00:04 UTC

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