1. Computer Science Department, INSA Lyon, 20 avenue Albert Einstein, Villeurbanne, Cedex 69621, France
2. Graduate School of System Informatic, Kobe University, 1-1 Rokko-dai, Nada-ku, Kobe 657-8501, Japan
3. Department of Computational Science, Kobe University, 1-1 Rokko-dai, Nada-ku, Kobe 657-8501, Japan