Three ways: 1.A simple test for it 2. Use FD to deduce 3 Calculate closure of y Inferring FD's We are given FD's X1 -A1,X2->A2,.Xn-> A,and we want to know whether an FD Y-> B must hold in any relation (instance)that satisfies the given FD's. Example:If A->B and B->C hold,surely A->C holds,even if we don't say so. Important for design of good relation schemas. 1414 Inferring FD’s z We are given FD’s X1 -> A1, X2 -> A2,…, Xn -> An , and we want to know whether an FD Y -> B must hold in any relation (instance) that satisfies the given FD’s. – Example: If A -> B and B -> C hold, surely A -> C holds, even if we don’t say so. z Important for design of good relation schemas. Three ways: 1. A simple test for it 2. Use FD to deduce 3. Calculate closure of y