Problem

Consider this query: Retrieve the Ssns of employees who work on at least those projects on...

Consider this query: Retrieve the Ssns of employees who work on at least those projects on which the employee with Ssn = 123456789 works. This may be stated as (FORALL x) (IF P THEN Q), where

x is a tuple variable that ranges over the PROJECT relation.


P ≡ employee with Ssn = 123456789 works on project x.


Q ≡ employee e works on project x.

Express the query in tuple relational calculus, using the rules

■ (∀ x)(P(x)) = NOT (∃x) ( NOT(P(x))).


■ (IF P THEN Q)≡(NOT(P) ORQ).

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