Database Systems: Concepts, Design and Applications

9.2. Functional Dependency (FD)

A functional dependency (FD) is a property of the information represented by the relation. It defines the most commonly encountered type of relatedness property between data items of a database. Usually, relatedness between attributes (columns) of a single relational table are considered. FD concerns the dependence of the values of one attribute or set of attributes on those of another attribute or set of attributes. In other words, it is a constraint between two attributes or two sets of attributes. An FD is a property of the semantics or meaning of the attributes in a relation. The semantics indicate how attributes relate to one another and specify the FDs between attributes. The database designer uses their ...