CSCI 431 Exam 1

There are several types of keys discussed in the sources.

Keys include:

* Superkey An attribute or a set of attributes that uniquely identifies a tuple within a relation.

* Candidate Key A superkey (K) such that no proper subset is a superkey within the relation. In each tuple of R, values of K uniquely identify that tuple (uniqueness) and no proper subset of K has the uniqueness property (irreducibility).

* Primary Key A candidate key selected to identify tuples uniquely within a relation.

* Alternate Key Candidate keys that are not selected to be a primary key.

* Foreign Key An attribute, or set of attributes, within one relation that matches a candidate key of some (possibly the same) relation. If a foreign key exists in a relation, then the foreign key value must match a candidate key value of some tuple in its home relation, or the foreign key value must be wholly null.

* Composite Key A candidate key that consists of two or more attributes.