
Chapter 10: A Logic-based Language for Database Updates 381
remark applies if it is desired to implement negation as negation by failure.
These issues are discussed in Manchanda [1987b].
View Updates
A database view is a rule-defined relation that is made to appear as a base rela-
tion to the user. The actual base relations used to define the view may be hid-
den from the user in the interest of brevity, security, and so on. A user's up-
date request on the view has to be translated down to the base relations and
then performed in such a way that the user sees the view relation as having
been updated. In general, a view defines a many-to-many