CP363 Lecture Notes - Lecture 20: Candidate Key, Functional Dependency, Superkey
8 Apr 2019
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Fd x->a then x is a superkey. How do we know what are the other candidate keys. Two fds exist in the relation teach. Fd2: instructor-> course (violating therefore not bcnf) {student,course} is a candidate key for this relation and that the dependencies shown follow the pattern in figure 14. 13 (b) So his relation is in 3nf but not bcnf. A relation is not in bcnf should not be decomposed so as to meet this property while possibly forgoing the preservation of all functional dependencies in the decomposed relation. We have to settle for sacrificing the functional dependency preservation. Test for checking non additivity of binary relational decompositions. The f. d (r1 intersection r2)->(r1-r2) is in f+ or. Fd (r1 intersection r2)->(r2-r1) is in f+ Let r be the relation not in bcnf let x be a subset of r and let x->a be the fd that causes a violation of bcnf then r may be decomposed into two relations.
