From: Wolfram Conen <conen@gmx.de>

Date: Fri, 26 Oct 2001 17:06:14 +0200

Message-ID: <3BD97BE6.32ECB0B1@gmx.de>

To: Karsten Tolle <tolle@dbis.informatik.uni-frankfurt.de>

CC: peter.crowther@networkinference.com, www-rdf-interest@w3.org

Date: Fri, 26 Oct 2001 17:06:14 +0200

Message-ID: <3BD97BE6.32ECB0B1@gmx.de>

To: Karsten Tolle <tolle@dbis.informatik.uni-frankfurt.de>

CC: peter.crowther@networkinference.com, www-rdf-interest@w3.org

Karsten Tolle wrote: > > Peter Crowther wrote: > ... > > Also, what do you do where the range of one is a superclass of the range > of > > the other, or where the ranges intersect? I see no particular reason to > > disallow these cases. > > > In the case we have a hierarchie of properties, e.g. p1 < p2. For my > personal feeling the subproperty p1 should not be alowed to be used with > resources the superproperty p2 is not allowed to. I see your motivation. However, as I tried to point out in the other email (sorry for the x type C...-error, must, of course, be y type C...), it is not anymore useful to think about range/domain "definitions" as constraints - so "allowed" is no longer a helpful term (with respect to my reception of the Model Theory Draft, www.w3.org/TR/rdf-mt/) > Therefore the domain (or > range) definition of the subproperty must be either equal or a subset > (subClassOf) of the domain (or range) definition of the superproperty. > When we allow cycles here the logical result would be that the domain and > range definitions must be equal. > Let's have a look at cycles for a moment: assume that you attach 3 range definitions to a property p p range C1 p range C2 p range C3 and also have a triple x p y From the model theory it follows that the schema-closure contains y type C1 y type C2 y type C3 Now, you may want to carry the same type information with three properties p1,p2,p3, that are related in a subProperty-Cycle and one range constraint per property: p1 supPropertyOf p2 p2 subPropertyOf p3 p3 subPropertyOf p1 p1 range C1 p2 range C2 p3 range C3 Now, you may use any one of the properties p1,p2,p3 to attach y to x, say x p2 y to precisely the same effect as before (for the reasoning see the previous email) y type C1 y type C2 y type C3 - however, you will also generate [x p1 y] [x p3 y], which is necessary to equalize the properties extensionally. Now, in a sense, you have simply "distributed" the three range definitions to three extensionally equivalent properties. This is (as far as the above is correct) what it is in the current "official" interpretation of RDF (as embodied in the RDF MT, where I can find not much ambiguity). As you see the question there is not whether you write down identic definitions of range/domain for properties in a subProperty cycle but to obtain a "correct" extension of the type property, which is pretty precisely what the schema closure makes sure. If this treatment of range/domain is really useful, is a different (but already closed) issue. Kindest regards, WolframReceived on Friday, 26 October 2001 11:06:46 GMT

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