De?ne the following concepts:
a. Key
b. Candidate key
c. Primary key
d. Superkey
a. A key, key(¯K ), associated with a relation schema, S, is a minimal (by inclusion) subset ¯K of attributes of S with the following property: An instance s of S satis?es key(¯K) if it does not contain a pair of distinct tuples whose values agree on al l of the attributes in ¯K .
b. Every key of a relation is also called a candidate key for that relation
c. One of the keys of a relation is designated as primary key.
d. A superkey is a set of attributes in a relation that contains a key of that relation
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