11
Datalog
•
Recall: a conjunctive query has the form:
q(
x
) =
9
y
1
…
9
y
k
.
f
(
x
,
y
)
where
f
is a conjunction of positive atomic
formulas
•
Example:
stands for
9
u.
9
v.(R(x,u)
Æ
R(u,v)
Æ
R(v,y))
q(x,y) :-
R(x,u), R(u,v), R(v,y)