D. Zeginis, Y. Tzitzikas, und V. Christophides. Proceedings of the 6th International Semantic Web Conference and 2nd Asian Semantic Web Conference (ISWC/ASWC2007), Busan, South Korea, Volume 4825 von LNCS, Seite 631--644. Berlin, Heidelberg, Springer Verlag, (November 2007)