M. Stonebraker, and L. Rowe. Memorandum, No UCB/ERL M86/85. Electronics Research Laboratory, College of Engineering, University of California, Berkeley 94720, (June 1987)
C. L�cluse, P. Richard, and F. Velez. Proceedings of the 13th Annual ACM Conference on
the Management of Data, page 424--433. Chicago, Illinois, (June 1988)