Re: Performance issues with OWL Reasoners => subclass vs instance-of

>>>>> "WB" == William Bug <William.Bug@DrexelMed.edu> writes:

  WB> CLASSes represent UNIVERSALs or TYPEs.  The TBox is the set of
  WB> CLASSes and the ASSERTIONs associated with CLASSes.

  WB> INSTANCEs represent EXISTENTIALs or INDIVIDUALs instantiating a
  WB> CLASS in the real world.  The ABox is the set of INSTANCEs and
  WB> the ASSERTIONs associated with those INSTANCEs.



I'd take a slight step back from this. You can think of classes and
instances in this way. But in the OWL sense, a class is a logical
construct with a set of computational properties. "Instances" is a
more difficult term. OWL actually has individuals. The instance store
uses "instances" because they are not really OWL individuals. 
There is also a philosophical concept of what a class is, what a
universal is an so on, which may be somewhat different, and is also
open to debate. 

  WB> Properly specified CLASSes are defined in the context of the
  WB> INSTANCEs whose PROPERTIES and RELATIONs they formally
  WB> represent.

  WB> Properly specified INSTANCEs are defined via their reference to
  WB> an appropriate set of CLASSes.

Think this would be circular. An OWL class is defined by the
individuals that it might have in any model which fits the
ontology. Not just the individuals it has an a specific model. 


  WB> Reasoners (RacerPro, Pellet, FACT++) generally have
  WB> optimizations specific to either reasoning on the TBox or
  WB> reasoning on the ABox, but it's difficult (i.e., no existing
  WB> examples experts such as Phil and others can cite) to optimize
  WB> both for reasoning on the TBox, the ABox AND - most importantly
  WB> - TBox + ABox (across these sets).

ABox is more complex than TBox, although I believe the difference is
not that profound (ie they are both really complex). For a DL as
expressive as that which OWL is based on, the complexities are always
really bad. In other words, no reasoner can ever guarantee to scale
well in all circumstances. This does not mean that you cannot build
reasoners which will scale well in practice. 


Make sense? 

Phil

Received on Friday, 15 September 2006 15:13:24 UTC