Department of Computing, City University, London, EC1V 0HB, UK. panos@alumni.doc.ic.ac.uk|Department of Computing, City University, London, EC1V 0HB, UK. panos@alumni.doc.ic.ac.uk|Department of Computing, City University, London, EC1V 0HB, UK. panos@alumni.doc.ic.ac.uk|Department of Computing, City University, London, EC1V 0HB, UK. panos@alumni.doc.ic.ac.uk|Department of Computing, City University, London, EC1V 0HB, UK. panos@alumni.doc.ic.ac.uk