Omer Rana Cardiff University

Department of Computer Science PO Box 916 Cardiff CF24 3XF United Kingdom

44 029 2087 4812 44 029 2087 4598 O.F.Rana@cs.cf.ac.uk http://www.cs.cf.ac.uk/department/staff/o.f.rana.shtml David Walker Cardiff University

Department of Computer Science PO Box 916 Cardiff CF24 3XF United Kingdom

44 029 2087 4205 44 029 2087 4598 David.W.Walker@cs.cf.ac.uk http://www.cs.cf.ac.uk/User/David.W.Walker/ Alex Gray Cardiff University

Department of Computer Science PO Box 916 Cardiff CF24 3XF United Kingdom

44 029 2087 4440 44 029 2087 4598 W.A.Gray@cs.cf.ac.uk http://www.cs.cf.ac.uk/department/staff/w.a.gray.shtml