 the arity of the
relations used. On the other hand we do have a more accurate model.

Regards  
      Matthew
===============================================================
Matthew West                    <A  HREF="http://www.matthew-west.org.uk/">http://www.matthew-west.org.uk/</A>

Principal Consultant                   Shell Visiting Professor
Operations &amp; Asset Management            The Keyworth Institute
Shell Services International            The University of Leeds
<A  HREF="http://www.shellser