RE: Property instantiation

Frank,

I think I got it now. Can't say that the resulting diagram (attached) says
more than a thousand words unless you spend a thousand words to explain it
to an outsider. 

Thanks for your help!

Regards,
Hans

-----Original Message-----
From: Frank Manola [mailto:fmanola@acm.org] 
Sent: Wednesday, April 19, 2006 19:22
To: Hans Teijgeler
Cc: 'SW-forum'
Subject: Re: Property instantiation

Hans Teijgeler wrote:
> Frank,
> 
> I wrote the code for the diagram "schema-basis", and tested that 
> against the W3C Validator:
> 
> <rdf:RDF
>     	xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
>     	xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
>     	xmlns:owl="http://www.w3.org/2002/07/owl#"
>     	xmlns="http://www.example.org/ex#"
>     	xml:base="http://www.example.org/ex">
> 
>     	<owl:ObjectProperty rdf:ID="hasAsPart"/>
> 
> 	<owl:Class rdf:ID="Foo">
>     		<rdfs:subClassOf rdf:resource="#UserDefinedClass"/>
>     		<rdfs:subClassOf>
>        		<owl:Restriction>
>           			<owl:onProperty rdf:resource="#hasAsPart"/>
>           			<owl:allValuesFrom rdf:resource="#Bar"/>
>        		</owl:Restriction>
>     		</rdfs:subClassOf>
> 	</owl:Class>
> 
> 	<owl:Class rdf:ID="Bar">
>     		<rdfs:subClassOf rdf:resource="#UserDefinedClass"/>
> 	</owl:Class>
> 
> 	<Foo rdf:ID="foo_1">
> 		<hasAsPart rdf:resource="#bar_1"/>
> 	</Foo>
> 
> 	<Bar rdf:ID="bar_1"/>
> 
> </rdf:RDF>
> 
> So it seems that the "schema-basis" diagram was correct. 

I wouldn't have said the diagram was "correct", because there are some
things in it that are puzzling, that is if it's supposed to be an RDF graph.

First, you have an arc between nodes labeled Foo and hasAsPart that has
neither a label nor an arrowhead.  Then there is an arc between nodes
labeled hasAsPart and Bar that has an arrowhead but no label.  I assume both
those arcs are meant to represent the allValuesFrom constraint, but that's
an unfamiliar diagrammatic convention to me;  in any case, in RDF graphs,
arcs have (property) labels and directions.

Second, at the individuals "level", you have an arc labeled type from the
hasAsPart arc up to the hasAsPart (class) node.  This type arc doesn't exist
in an RDF graph.

If you run the Validator again, have it generate the graph, and compare it
with your diagram, and you'll see what I mean.

The lesson, I think, is that a picture is only worth a thousand words to
someone who understands the diagrammatic conventions used in the picture,
since otherwise some additional words in explanation are necessary :-)

Yet you spoke about
> subclassing ObjectProperty, and that was the reason for the 
> "schema-basis-alternative" diagram. It puzzles me what you meant with
that.

I only mentioned subclassing ObjectProperty when I asked whether that was
what you were trying to do.

--Frank

> 
> Regards,
> Hans
> 

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