G. Hjaltason, and H. Samet. SSD '95: Proceedings of the 4th International Symposium on Advances in Spatial Databases, page 83--95. London, UK, Springer-Verlag, (1995)
G. Moerkotte. VLDB '98: Proceedings of the 24rd International Conference on Very Large Data Bases, page 476--487. San Francisco, CA, USA, Morgan Kaufmann Publishers Inc., (1998)
M. Hernández, and S. Stolfo. SIGMOD '95: Proceedings of the 1995 ACM SIGMOD international conference on Management of data, page 127--138. New York, NY, USA, ACM, (1995)