Department of Information Technology and TUCS, University of Turku, FI-20014 Turku, Finland. jotatu@utu.fi|Department of Information Technology and TUCS, University of Turku, FI-20014 Turku, Finland. jotatu@utu.fi|Department of Information Technology and TUCS, University of Turku, FI-20014 Turku, Finland. jotatu@utu.fi|Department of Information Technology and TUCS, University of Turku, FI-20014 Turku, Finland. jotatu@utu.fi