Re: looking for a social schema

Hi Heiko,

On Fri, Nov 18, 2011 at 4:33 AM, Heiko Paulheim
<paulheim@ke.tu-darmstadt.de> wrote:
> Due to the open world assumption, the value of that counter would (probably)
> we wrong.
>
> If I have
> :Peter foaf:knows :Stephen .
> :Peter foaf:knows :Marc .
>
> and, based on that knowledge, I added
>
> :Peter myschema:friendnb "2"^^xsd:integer .
>
> this would not be a valid conclusion - there may be a lot more friends of
> Peter which are not in my knowledge base (don't we all have friends without
> a facebook account?), and :Stephen and :Marc might even refer to the same
> person. In other words, with that approach, I would add knowledge to my
> knowledge base which is potentially wrong.

While you are correct in saying that the inference of 2 friends is
invalid, the idea of cardinality is not inconsistent with the open
world assumption (OWA). Melvin's original question was about a
property that can be used to declare cardinality, and this is fine
with the OWA. Indeed, OWL uses it.

So, for instance, if you declare:

 :Peter myschema:friendnb "2"^^xsd:integer .

and then you say:

 :Peter foaf:knows :Stephen .
 :Peter foaf:knows :Marc .
 :Stephen owl:differentFrom :Marc .

Then you know that we have identified all the friends of :Peter. This
does not preclude another statement of the form:

 :Peter foaf:knows :Steve .

But since we already knew all of :Peter's friends, then we know that
this new statement must refer to an alias for one of the existing
friends.

Taking it further:

 :Steve owl:differentFrom :Marc .

Means that:

 :Steve owl:sameAs :Stephen .

All of this is just a long-winded way of explaining that a cardinality
predicate is not in conflict with the open world assumption. However,
it works with different use cases than with the closed world.
Specifically, under the OWA you cannot derive the current cardinality,
but you can declare it.

Regards,
Paul Gearon

Received on Friday, 18 November 2011 15:49:15 UTC