Department of Information Technology, University of Turku, Turku Centre for Computer Science (TUCS), Joukahaisenkatu 3-5, 20520 Turku, Finland. jari.bjorne@utu.fi|Department of Information Technology, University of Turku, Turku Centre for Computer Science (TUCS), Joukahaisenkatu 3-5, 20520 Turku, Finland. jari.bjorne@utu.fi|Department of Information Technology, University of Turku, Turku Centre for Computer Science (TUCS), Joukahaisenkatu 3-5, 20520 Turku, Finland. jari.bjorne@utu.fi