School of Computing Science, University of Newcastle, Newcastle upon Tyne, UK. L.J.Steggles@ncl.ac.uk|School of Computing Science, University of Newcastle, Newcastle upon Tyne, UK. L.J.Steggles@ncl.ac.uk|School of Computing Science, University of Newcastle, Newcastle upon Tyne, UK. L.J.Steggles@ncl.ac.uk|School of Computing Science, University of Newcastle, Newcastle upon Tyne, UK. L.J.Steggles@ncl.ac.uk