Re: on behalf of sandro

From: Sandro Hawke (
Date: 10/24/01

> Richard Fikes wrote:
> > >The knowledge base contains the statements: "Pat's car is blue, and
> > >there is something colored red."  Somewhat more formally:
> > >
> > >   RDF(PatsCar, color, blue).
> > >   exists x (RDF(x, color, red)).
> >
> > Sorry to be dense, but how does one state "there is something colored
> > red" in DAML+OIL?

Deborah McGuinness wrote:
> there are a few ways, arguably, none perfect.
> the most direct is mincardinalityQ
> state that something has mincardinality 1 (or more)
> and the Q in this case is RED-THING
>  Deborah L. McGuinness

There is a much simpler way, since RDF includes existential variables.

    <rdf:RDF xmlns:rdf=""
        <example:color rdf:resource=""/>

This is parsed by the validator [1] to 

    _:j70241 <> <> .

As Pat's model theory [2] (and his various e-mails to me on
www-rdf-rules) make clear, the "unlabeled" nodes (like _:j70241)
should be interpretted as existential variables.

This clarification to RDF is fairly recent, and not yet official,
(it's just a working draft), but I haven't heard anyone objecting yet.
I have heard several members of the original RDF group say this is
what they meant.   

    -- sandro


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