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Re: RDF Issue rdfs-clarify-subClass-and-instance

From: graham wideman <graham@wideman-one.com>
Date: Thu, 29 Aug 2002 16:57:33 -0700
Message-Id: <4.1.20020829161739.0168bf08@sunstroke.sdsu.edu>
To: Frank Manola <fmanola@mitre.org>
Cc: Brian McBride <bwm@hplb.hpl.hp.com>, www-rdf-comments@w3.org, phayes@ai.uwf.edu

Frank:

Again, thanks for taking the time to try to wade through this.  

>But the rules don't say what you must do with this information.

I completely accept this.  I believe it when you say that RDF does not prescribe that rdfs:domain information to be used as constraints.  This is *not* the issue.

The issue is that RDF docs say that rdfs:domain *may* be used by an app that wishes to use them to establish constraints.  I believe that the semantics of rdfs:domain as prescibed by RDFS are such the it *cannot* be used for constraints.

You say:
> Certainly it's possible (and not a 
>"violation" of RDFS) to build an application that would use the example 
>information we've been discussing to conclude that what someone's said 
>about Garfinkle having an author must be wrong.

I'm saying that I don't think it is possible to use RDFS this way, and I'm challenging someone to show how to do it.

Reduced to bare minimum, I want to see how in RDFS you *can* employ RDFS to provide schema information to support an app that wants to implement the following most basic of constraints:

-- Instances can only have properties that we say that they can have.
-- Instances of class Book have property Author

... and is then confonted with the following...

An instance Garfinkleof Cat arrives with property Author.  
The app has seen no prior assertion of either:
  Instances of class Cat have property Author ... or...
  Class Cat is a subClass of Book
App concludes this is an error.

I just do not see how rdfs:domain can be used in even this basic way. If the answer supposedly involves:

Book rd:type Class
  Property rdfs:domain Author

... then what I read of the RDFS specs tells my app that it's required to conclude that Garfinkle is a Book.  This does not appear to me to be optional. 

The only optional part is whether my app uses RDFS schema info to implement constraints *at all*. If it wants to implement constraints, then at the point where it receives "Garfinkle has an Author property", the app is looking at an RDFS collection of facts where RDFS rules have already concluded that Garfinkle is a Book.

If you do see how to do this, or know where it's been done, I'd love to see it. 

You also note that:

>There are a number of existing applications that use 
> (I assume "usefully") RDFS to define their structures,

... could you point me to some of these (ie: apps that employ RDFS to support constraint functionality)?

Thanks,

Graham

---------------------------------------------------
Graham Wideman
Resources for programmable diagramming at:
http://www.diagramantics.com
graham@wideman-one.com
http://www.wideman-one.com
Received on Thursday, 29 August 2002 19:59:47 GMT

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