1. University of Wolverhampton, School of Humanities, Language and Social Sciences, Stafford Street, Wolverhampton WV1 1SB, UK.
2. IBM T. J. Watson Research Center, 30 Saw Mill River Road, Hawthorne, NY 10532, USA.
3. King's College, London, Department of Computer Science, King's College, The Strand, London WC2R 2LS, UK.