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Proposed response to: e: Restriction, DeprecatedClass in OWL Language Reference 31 March 2003

From: Guus Schreiber <schreiber@cs.vu.nl>
Date: Tue, 24 Jun 2003 14:24:36 +0200
Message-ID: <3EF84304.50207@cs.vu.nl>
To: WebOnt WG <www-webont-wg@w3.org>

Richard H. McCullough wrote:
http://lists.w3.org/Archives/Public/public-webont-comments/2003May/0090.html

> From: "Richard H. McCullough" <rhm@cdepot.net>
> Subject: Re: Restriction, DeprecatedClass  in OWL Language Reference 31 March 2003
> 
> 
> So your class hierarchy is
> 
>     rdfs:Class
>         owl:Class
>         owl:Restriction
>         owl:DeprecatedClass

Sorry if the previous message was not clear enough. The class hierarchy 
is (see Appendix B of Reference)

rdfs:Class
     owl:Class
         owl:Restriction
     owl:DeprecatedClass

So, owl:Restriction is a specific kind of owl:Class.

> 
> That raises several questions in my mind.
> 1. Shouldn't you strive for
>     owl:Class  owl:sameAs  rdfs:Class

This is true in a weaker sense in OWL Full (owl:Class 
owl:equivalentClass rdfs:Class), but not in OWL DL. See the note in Sec. 
3.1 in the editor's draft of OWL Reference [1]:

[[
NOTE: owl:Class is defined as a subclass of rdfs:Class. The rationale 
for having a separate OWL class construct lies in the restrictions on 
OWL DL (and thus also on OWL Lite), which imply that not all RDFS 
classes are legal OWL DL classes. In OWL Full these restrictions do not 
exist and therefore owl:Class and rdfs:Class are equivalent in OWL Full.
]]

> 2. Shouldn't owl:Restriction be a metaclass of rdf:Property?
>     owl:Restriction  rdfs:subClassOf  rdf:Property

owl:Restriction is not a property, it is a class description of which 
the class extension is defined in terms of property constraints. See 
Sec. 3.1.2:

[[
The class owl:Restriction is defined as a subclass of owl:Class. A 
restriction class should have exactly one triple linking the restriction 
to a particular property, using the  owl:onProperty property. The 
restriction class should also have exactly one triple that represents 
the value constraint c.q. cardinality constraint on the property under 
consideration, e.g., that the cardinality of the property is exactly 1.
]]

> 3. Likewise, shouldn't these be subClasses of rdf:Property
>      owl:DataRange

This is not a property, but a class that can act as a datatype. See Sec. 
6.2:

[[
In the case of an enumerated datatype, the domain value of owl:oneOf is 
a blank node of class owl:DataRange ....
]]

>      rdfs:Datatyp
 >      rdfs:Literal

This is outside the scope of the OWL specifications. I would think this 
is not the case, however.

>      owl:DeprecatedProperty

Correct, see Appendix B:

[[
<rdfs:Class rdf:ID="DeprecatedProperty">
   <rdfs:label>DeprecatedProperty</rdfs:label>
   <rdfs:subClassOf rdf:resource="&rdf;Property"/>
</rdfs:Class>
]]

> 4. It would be desirable to define an owl:Entity class,
> disjoint from rdf:Property, which would include as subClasses
>     owl:AllDifferent
>     rdfs:Container
>     owl:DeprecatedClass
>     owl:Enumeration
>     owl:Intersection
>     rdf:List
>     owl:Ontology
>     owl:Union
> 5. The above would produce the Class hierarchy
>     owl:Thing
>         owl:Entity
>         rdf:Property
>         rdf:Statement
> where Entity,Property,Statement are disjoint and exhaustive.
> This hierarchy is very meaningful, from both  metaphysical
> and epistemological viewpoints.
> Entity is the class of primary things that exist.
> Property is the class of Entity properties plus meta properties
>     (properties of things other than entities).
> Statement is the class of relations between things.

I;m not completely sure about the rationale for introducing owl:Entity. 
I would suggest to discuss this issue at the rdf-logic@w3.org discussion 
list.


Thanks for your comments. Please let us know whether this response is 
satisfactory.

Guus Schreiber

> 
> Dick McCullough
> knowledge := man do identify od existent done;
> knowledge haspart proposition list;


-- 
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E-mail: schreiber@cs.vu.nl
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Received on Tuesday, 24 June 2003 08:24:37 GMT

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