The "bounding expression" would be the fact that we were doing an intersection
with A at a higher level. My question was whether there was any optimization
that would take that into account.
I don't fully follow everything you are saying...
A few questions:
1. Is there a way to compute set difference (A - B) ?
2. Is there a way in a owl:Restriction on a property to state there are no
values from a set.
Essentially a negation on owl:someValuesFrom.
I want to get all items that are have a property with values from A, but not
from B.
-----Original Message-----
From: Dave Reynolds [mailto:[email protected]]
Sent: Tuesday, September 13, 2011 3:52 AM
To: [email protected]
Subject: Re: set difference
On Mon, 2011-09-12 at 15:49 +0000, David Jordan wrote:
> I want to express set difference in OWL, I was a bit surprised that this is
> not directly supported.
> I’d be interested in hearing whether the following would work, and how
> efficient it will be to compute.
> Assume you have sets A and B.
> I can define the union and intersection of A and B in OWL, we can call them
> AUB and AIB, respectively.
> Then I am guessing that A – B would be defined as follows:
> A_B owl:intersectionOf (
> A
> [ a owl:Class ; owl:complementOf AIB ] ).
>
> My big concern is the computing of the owl:complementOf AIB.
> Is the implementation going to take into account that the outer expression is
> doing an intersection with A, so that it strictly takes the elements in AIB
> and subtracts them from A?
In the case of Jena rules then irrelevant because we don't support complementOf
:)
For an mythical OWL full reasoner that attempted to aggressively materialize
inferences then the extension of the b-node would be part of the closure. But
in general you can't enumerate a complementOf anyway unless there is some
bounding expression (remember the Open World assumption).
For a DL reasoner that it should treat the b-node simply as syntax and will be
attempting to prove membership of the (A intersect (¬B)) expression.
Dave
