A superclass is any combination of attributes that must be unique to all possible values of a relation.
The candidate key is a minimal superkey. Minimal means that if any attribute of the superclap has been deleted, then the remaining set of attributes will no longer be a superkey, i.e. The uniqueness property will be lost. In other words, each superkey consists of a candidate key plus zero or more other attributes.
A component key, also called a composite key, is a candidate key that has more than one attribute.
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