R. Fagin, P. Kolaitis, R. Miller, and L. Popa. Database Theory - ICDT 2003, 9th International Conference,
Siena, Italy, January 8-10, 2003, Proceedings, page 207-224. (2003)
L. Popa, Y. Velegrakis, R. Miller, M. Hernández, and R. Fagin. VLDB 2002, Proceedings of 28th International Conference
on Very Large Data Bases, August 20-23, 2002, Hong Kong,
China, page 598-609. (2002)