W3C home > Mailing lists > Public > public-powderwg@w3.org > December 2007

Re: URI groups

From: Andrea Perego <andrea.perego@uninsubria.it>
Date: Thu, 06 Dec 2007 18:03:55 +0100
Message-ID: <47582B7B.1020301@uninsubria.it>
To: public-powderwg@w3.org

Hi, Stasinos.

I agree that wdr:includeHost is something odd for OWL, but, as I've
already said, there exist RDF/OWL vocabularies defining properties for
pattern matching, like SWRL and N3/Cwm built-ins [1,2].

Why cannot we use them?

For example:

<owl:Class rdf:ID="ResourceOnExampleDotOrg">
      <owl:onProperty rdf:resource="&log;uri" />
      <owl:hasValue rdf:parseType="Resource">


- &log;uri is a N3/Cwm built-in [2] which returns the URI of the
  subject; e.g.

    <owl:Class rdf:ID="ResourceOnExampleDotOrg">

  where http://www.example.org/ is the URI of the RDF document
  containing these lines;

- string:matches is a N3/Cwm built-in, where "the object is is a regular
  expression in the perl, python style" [2]

- [regEx] is a regular expression matching the the URIs having where the
  host component ends with "example.org"



Stasinos Konstantopoulos wrote:
> Dear POWDER,
> just my couple of cents on the URI groups issue. (This has nothing to do
> with the equivalence vs subsumption thread.)
> Andrea's proposal (current URI group document) looks like this:
> <owl:Class rdf:ID="ResourceOnExampleDotOrg">
>   <owl:equivalentClass>
>     <owl:Restriction>
>       <owl:onProperty rdf:resource="&wdr;includeHost" />
>       <owl:hasValue>example.org</owl:hasValue>
>     </owl:Restriction>
>   </owl:equivalentClass>
> </owl:Class>
> (it doesn't really matter if it's going to be an implication or an
> equivalence, the latter simply promises that there is no other way to
> be in the ResourceOnExampleDotOrg class, like a DNS alias or
> something.)
> Now, I have already voiced my concerns about this approach on telcos
> and emails, and I think I should re-iterate it, just for clarity's
> sake. In a nutshell, it a well-known fact that once concrete domains
> are added (strings, regexps, integers, and the like) it get really
> hard to come up with a complete deductive operator and the RDF graphs
> cannot be closed (ie, automatically generate the graph where all
> implicit facts have been made explicit.)
> In other words, there are important axioms defining the domain of URIs
> that cannot be expressed in OWL, e.g. that a resource with value
> "X.Y.Z" for its "includeHost" property also has value "Y.Z" and "Z"
> for the same property. The domain of URIs cannot be closed under OWL,
> because OWL is not expressive enough to imply property values given
> other property values.
> For this reason, the fact that ResourceOnExampleDotOrg has been
> axiomatically defined in our example here isn't of much use, as it
> pretends to specify all and every instances that are in the class,
> where, in fact, it cannot.
> My proposal is that URI Groups are defined in pretty much the same way
> as reification: they're there, but not within the logic. Something
> along the lines of:
>   <owl:Class rdf:about="#FOSIchildSafe">
>     <rdfs:subClassOf rdf:ID="CSassertion" rdf:resource="#ChildSafe"/>
>   </owl:Class>
>   <rdf:Statement rdf:about="#CSassertion">
>     <foaf:maker rdf:resource="http://www.example.org/foaf.rdf#me"/>
>   </rdf:Statement>
>   <rdf:Statement rdf:about="#CSassertion">
>     <wdr:includeHost "example.org"^^xsd:string/>
>   </rdf:Statement>
> This way we say nothing about subsumption or equivalenc and the such,
> and an external, POWDER-specific tool will go over the DR and
> explicitly add a resource to the FOSIchildSafe class, if appropriate.
> OWL subsumption will then say that such a resurce is also ChildSafe.
> BTW, with OWL semantics out of the way, one can possibly even go back
> and throw excetions and excludeHost statements back into the game.
> Hope this helps a bit,
> stasinos
Received on Thursday, 6 December 2007 16:59:14 UTC

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