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The key is actually AE. The proof is simple, a key for definition is a minimal set of attributes whose closure contains all the attributes of the table. If you calculate the closure of A with respect to the given functional dependencies you will find: A+ = {ABCD} that does not contain the attribute E. So A is not a key, and E must be present in any key of ...


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AIUI, the relational model is a mathematical ideal. No vendor implements in its entirety. Check out Dataphor if you want that sort of system. To show how easy it is to subvert the relational model - just do SELECT Surname FROM Telephone_Directory; Here in Ireland, you'll get hundreds of O'Briens and Murphys - the result is a still a table, although ...



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