C. Morbidoni, G. Tummarello, O. Erling, and R. Bachmann-Gmür. Proceedings of the 6th International Semantic Web Conference and 2nd Asian Semantic Web Conference (ISWC/ASWC2007), Busan, South Korea, volume 4825 of LNCS, page 533--546. Berlin, Heidelberg, Springer Verlag, (November 2007)