U. Riss, U. Cress, J. Kimmerle, and S. Martin. Proceedings of KMAC2006, The Third Knowledge Management Aston Conference, Operational Research Society, Birmingham, (2006)
X. Dong, A. Halevy, and J. Madhavan. SIGMOD '05: Proceedings of the 2005 ACM SIGMOD international conference on Management of data, page 85--96. New York, NY, USA, ACM Press, (2005)