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databasefunctional-dependencies

Functional Dependency query

Say I have a relation called PAPER = {ID, Title, Description, No.Students, Quarter}.

If I say ID -> Title and {Title, Quarter} -> No.Students. Is there an axiom that permits me to say {ID, Quarter} -> No.Students?

Because if id determines title, can't I just replace title with id in the second functional dependency?

Solution

  • One of the additional rules derived from Armstrong's axioms is the rule of pseudo-transitivity. It states that 

    If A->B and BC->D then AC->D.

    Substituting your terms . . .

    If ID->Title and {Title, Quarter}->No.Students, then {ID, Quarter}->No.Students