Department of Information Technology, University of Turku, Turku, Finland. mirva.piippo@utu.fi|Department of Information Technology, University of Turku, Turku, Finland. mirva.piippo@utu.fi|Department of Information Technology, University of Turku, Turku, Finland. mirva.piippo@utu.fi|Department of Information Technology, University of Turku, Turku, Finland. mirva.piippo@utu.fi|Department of Information Technology, University of Turku, Turku, Finland. mirva.piippo@utu.fi