COP 4710 Lecture Notes - Lecture 6: Functional Dependency, Multivalued Dependency, Superkey

• School: FIU
• Department: Computer Programming
• Course: COP 4710
• Professor: Ivanoski

Document Summary

Bcnf rules = x y is a trivial functional dependency (i. e. , y is a subset of x) It is not always possible to get a bcnf decomposition that is dependency preserving. Let r be a relation schema with a set of attributes that are partitioned into 3 nonempty subsets. We say that y z (y multidetermines z )if and only if for all possible relations r (r ) < y1, z1, w1 > e r and < y1, z2, w2 > e r. < y1, z1, w2 > e r and < y1, z2, w1 > e r. Note that since the behavior of z and w are identical it follows that. Y z if y w. In example: course teacher course book. If y z then y z. Indeed we have (in above notation) z1 = z2 the claim follows. To test relations to determine whether they are legal under a given set of.