What is the smallest number of attributes a relation key can have? A table, ABC,

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What is the smallest number of attributes a relation key can have? A table, ABC, has attributes A, B, and C, and a function dependency A rightarrow BC. Write an SQL CREATE ASSERTION statement that prevents a violation of this functional dependency. Prove that every 3NF relation schema with just two attributes is also in BCNE Prove that every schema that has at most one nontrival FD is in BCNE If the functional dependency X rightarrow Y is a key constraint, what are X and Y? Can a key be the set of all attributes if there is at least one nontrivial FD in a schema? The following is an instance of a relation schema. Can you tell whether the schema includes the functional dependencies A rightarrow B and BC rightarrow A? Prove that Armstrong's transitivity axiom is sound--that is, every relation that satisfies the FDs X- rightarrow Y - and Y - rightarrow Z- must also satisfy the FD X- rightarrow Z-. Prove the following generalized transitivity rule: if Z- Y-, then X- rightarrow Y- and Z- rightarrow W- entail X- rightarrow W-. Try to prove this rule in two ways:

Explanation / Answer

Dear... Given the relation schema R( A,B, C) 1. AB -> C 2. A -> B -> C 3. A -> B & C-> A 4. BC -> A

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