1. Department of Computer Science, King's College London, London WC2R 2LS, UK
2. Digital Ecosystems and Business Intelligence Institute, Curtin University, GPO Box U1987 Perth WA 6845, Australia
3. School of Electrical Engineering and Computer Science, The University of Newcastle, Callaghan NSW 2308, Australia
4. Department of Mathematics, University of West Bohemia, Pilsen, Czech Republic