- From: Phillip Lord <phillip.lord@newcastle.ac.uk>
- Date: Fri, 15 Sep 2006 16:13:04 +0100
- To: William Bug <William.Bug@DrexelMed.edu>
- Cc: "Kashyap, Vipul" <VKASHYAP1@PARTNERS.ORG>, "chris mungall" <cjm@fruitfly.org>, <semantic-web@w3.org>, <public-semweb-lifesci@w3.org>
>>>>> "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