# Expressiveness question

From: Sheila McIlraith <sheila@cs.toronto.edu>
Date: Wed, 17 Dec 2003 15:42:40 -0500

Message-Id: <03Dec17.154242edt.453294-19219@jane.cs.toronto.edu>
```
Hi all,

The following question arose from an OWL-S [1] Coalition discussion
regarding development of a process model for Web services (WS).  OWL alone
is not sufficiently expressive to capture all and only the intended
interpretations of a WS process model, and we're investigating whether
SWRL may be.

To this end, we are asking whether  we can axiomatize a situation
calculus [2] domain theory in SWRL.  The situation calculus
calculus is a first-order logical language for reasoning about
action and change.  It has proven sufficiently expressive for
axiomatizing a Web service process model, and we wondered whether
such a process model could be expressed in SWRL.  If not, can
SWRL be extended to axiomatize a situation calculus domain theory?

To this end, the following is an example of an axiom we would like
to encode:

Forall x. Forall s.
holding(x,do(a,s)) iff
[(a=pickup(x)) V (holding(x,s) & (a neq putdown(x))]

Legend:
- do is a function that maps actions (a) and situations (s) into
new situations (s).
- V is "or"
- neq is "not equal"
- iff is "if and only if"

This axiom says
<a robot is> holding x in the situation resulting from
performing action a in situation s (i.e., "do(a,s)") if and only if
- the action was "pickup(x)"
OR
- <the robot was> holidng x is situation s, and the action was
not "putdown(x)"

[1] OWL-S is the an OWL ontology for services
http://www.daml.org/sevices

[2] The situation calculus is a first-order language for reasoning
about action and change.  It can originally be credited to McCarthy
and Hayes.  Reiter was central in extending the language and renewing
interest in its use.

"Knowledge in Action: Logical Foundations for Specifying
and Implementing Dynamic Systems"
Raymond Reiter, 2001, The MIT Press, Cambridge, Mass.

Thanks,
Sheila

----------------------------------------------------------------------
Sheila McIlraith
Department of Computer Science
University of Toronto