Institute of Informatics, Silesian Univ. of Technology, Akademicka 16, Gliwice, 44-100, Poland. lukasz.wrobel@polsl.pl.|Institute of Informatics, Silesian Univ. of Technology, Akademicka 16, Gliwice, 44-100, Poland.|Institute of Innovative Technologies, EMAG, Leopolda 31, Katowice, 40-189, Poland.