BioHealth and Information Management Groups, School of Computer Science, University of Manchester, Oxford Road, Manchester, UK, M13 9PL. Robert.Stevens@manchester.ac.uk|BioHealth and Information Management Groups, School of Computer Science, University of Manchester, Oxford Road, Manchester, UK, M13 9PL. Robert.Stevens@manchester.ac.uk|BioHealth and Information Management Groups, School of Computer Science, University of Manchester, Oxford Road, Manchester, UK, M13 9PL. Robert.Stevens@manchester.ac.uk