S. Trißl, and U. Leser. SIGMOD '07: Proceedings of the 2007 ACM SIGMOD international conference on Management of data, page 845--856. New York, NY, USA, ACM, (2007)
M. Gemis, and J. Paredaens. Object Technologies for Advanced Software, First JSSST International Symposium, 742, page 339--355. Kanazawa, Japan, (November 1993)