Define union compatibility, Database Management System

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Define union compatibility? Explain why INTERSECTION of two relations cannot be performed if they are not union compatible?

Two relations R(A1, A2,-------, An) and S(B1, B2,-----, Bn) are said t union compatible if they have the similar degree n and if dom (A) = dom(B) for all i=1---ni i Intersection needs two relations to be union compatible since or else it is not probable to formulate the criterion as to on what basis will attributes be considered as general.

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