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Re: OWL-S: simple proposal to evolve logic expressions

From: Bijan Parsia <bparsia@isr.umd.edu>
Date: Fri, 20 May 2005 01:56:44 +0900
Message-Id: <533f51290d6c4af0a1f76faaa93adabb@isr.umd.edu>
Cc: public-sws-ig@w3.org, David Martin <martin@AI.SRI.COM>
To: Daniel Elenius <daele@ida.liu.se>

On May 20, 2005, at 1:36 AM, Daniel Elenius wrote:

> David Martin wrote:
[snip]
>> --- Proposed change (4):
>>
>> Restrict range of expressionContent:
>>   for SWRL-Expression range = union of Imp, AtomList, and Atom
>
> Not Imp, I think. Imps don't "evaluate" to true or false

What?

http://www.daml.org/2003/11/swrl/abstract.html

"""Informally, a rule may be read as meaning that if the antecedent 
holds (is "true"), then the consequent must also hold. An empty 
antecedent is treated as trivially holding (true), and an empty 
consequent is treated as trivially not holding (false). Rules with an 
empty antecedent can thus be used to provide unconditional facts; 
however such unconditional facts are better stated in OWL itself, i.e., 
without the use of the rule construct."""

>  (they're not quite implications in the "logical connectives" sense).

How not?

http://www.daml.org/2003/11/swrl/direct.html#3.1

"""A binding B(Ι) satisfies an antecedent A iff A is empty or B(Ι) 
satisfies every atom in A. A binding B(Ι) satisfies a consequent C iff 
C is not empty and B(Ι) satisfies every atom in C. A rule is satisfied 
by an interpretation Ι iff for every binding B such that B(Ι) satisfies 
the antecedent, B(Ι) also satisfies the consequent.

The semantic conditions relating to axioms and ontologies are 
unchanged. In particular, an interpretation satisfies an ontology iff 
it satisfies every axiom (including rules)"""

http://www.daml.org/2003/11/swrl/examples.html

"""An even simpler rule would be to assert that Students are Persons, 
as in Student(?x1) ⇒ Person(?x1).

Implies(Antecedent(Student(I-variable(x1)))
         Consequent(Person(I-variable(x1))))
However, this kind of use for rules in OWL just duplicates the OWL 
subclass facility. It is logically equivalent to write instead

Class(Student partial Person)
or

SubClassOf(Student Person)"""

If you look at :	
	http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#3.3

You'll see the interpretation of the owl variants.

Rules in SWRL are just material conditionals. They most certainly 
"evaluate" to true or false. They may be inferred.

>  In fact, it may be easier to just do AtomLists (if there's a single 
> Atom, then we just have a list with one element).

Prolly true. But if Preconditions are just formulae (rather than 
restricted to conjunctions), there's no need to avoid imps.

Cheers,
Bijan.
Received on Thursday, 19 May 2005 17:20:44 UTC

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