Re: modelling issue?

On Sep 29, 2009, at 4:22 AM, <tim.glover@bt.com> wrote:

>
>
> <=============
>
> Furthermore,  it is perfectly legal to declare the domain of a  
> property
> more than once, such as:
>
>    P rdfs:domain GreenItems .
>    P rdfs:domain BlueItems .
>
> Then if you write a statement like:
>
>    x P y .
>
> the domain declarations imply that x is in both GreenItems and
> BlueItems.
>
> =============>
>
> OK...
>
> <============
>
> Note that the effect is that the domain of P is the
> *intersection* of GreenItems and BlueItems -- not the union.
>
> ============>
>
>
> OK, but personally I found the terms intersection and union a bit
> confusing in this context. Just to clarity... In an assertional  
> language
> like RDFS it is not possible to place any restrictions on anything by
> adding a new triple.

? Sure it is. In fact, adding any triple always places restrictions  
upon something, in a sense. It constrains the property to hold between  
the subject and object.

>   So, adding
>
> x P y
>
> asserts that x is in both GreenItems and BlueItems, but adding
>
> P rdfs:domain BlueItems
>
> in no way implies that the domain of P is smaller than the set of
> GreenItems... Is that right?

No, not right. It implies that the domain is (a subclass of, as  
Bernard correctly points out) the intersection of BlueItems and  
GreenItems. These domains and range statements are *constraints*  
rather than declarations, so when you say two of them, they both  
apply. So if BlueItems and GreenItems are both domains of P, then x P  
y. implies that x is in both of these classes, which means it is in  
their intersection.

Pat

>
> Tim Glover
>
>

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Received on Tuesday, 29 September 2009 15:41:06 UTC