Evaluation

BOTTOM-UP-EVALUATE(r1...rn)

While some Ri' - Ri is not empty

Forall i

Ri = UNION(Ri,Ri')

Foreach rule

say the rule is rj(X) <= expr(X,Y).

Rj' =UNION(Rj', PROJECT(X,

EVAL(emptyTable, expr(X,Y))))

• EVAL takes a table and an expression; returns a table.

• The empty table has no attributes, and ONE tuple with zero elements.

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