Copyright © 1993 Rickard E. Faith (faith@cs.unc.edu). All rights reserved. Permission is granted to make and distribute verbatim copies of this paper provided the copyright notice and this permission notice are preserved on all copies.This is (with the author's explicit permission) a modified copy of the original document. If you wish to reproduce just this section, you are advised to get the original version by ftp from ftp.cs.unc.edu:/pub/faith/papers/scsi.paper.tar.gz