Unformatted text preview: gic to get rid of existential variables.
2. Invert the view de nitions, so they are EDB
predicates with function symbols de ned in
terms of a view.
3 Remember that the EDB" predicates are
really global, abstract concepts as in IM,
not stored relations. Example To invert the view
v1X,Y :- parX,Z & parZ,Y 1 we get:
parX,fX,Y :- v1X,Y
parfX,Y,Y :- v1X,Y Notice that :- is a misnomer as far as the
view de nition is concerned, but in the inverse
rules it is simply an assertion that there are
no bogus facts in the view. A More Complex Example
Suppose we have EDB predicates global concepts
f X; Y and mX; Y , meaning that Y is the
father or mother, respectively, of X .
Our query is to nd all maternal ancestors"
of an individual X , i.e., all females who are
r1: mancX,Y :- mX,Y
r2: mancX,Y :- fX,Z & mancZ,Y
r3: mancX,Y :- mX,Z & mancZ,Y
The available views are:
v1X,Y :- fX,Z & mZ,Y
v2X,Y :- mX,Y Invert the Views
r4: fX,gX,Y :- v1 X,Y
r5: mgX,Y,Y :- v1 X,Y
r6: mX,Y :- v2...
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- Spring '09
- SEPTA Regional Rail, function symbols