
Chapter 10: A Logic-based Language for Database Updates 387
2.
The translator
(~p
v
(t))
D is semantically acceptable in Δ if for all
variable assignments s, for all 7,7 Ε S, if (7,7) Ε Λ^(—p
v
(f)M) and 7(=
-!P
v
(0M then 7 = 7. •
For example consider the following delete translator η for the edp view.
η
:
(-edp
(
Ename, Dept, Proj
) >
(-ed(Ename,Dept))
(
(-ep(Ename,Proj)>
)
For all values of Ename, Dept, and
Proj,
η returns a state (say 7) in which
—ι ep(Ename, Proj ) is true. Recall that the completion of the view definition
is true in every state in an M-model. If
—j
ep( Ename, Proj ) is true in 7, then
the completion of the edp view implies