Question

For the relation schema Player (ID, Name, Birthday, Address, Email, PhoneNumber, PlayPos) assume that ID is the primary key and no Player’s names are the same (i.e., a Players’s name can uniquely identify a Player).
1. Please write down all the non-trivial functional dependencies that hold in the schema Player.

2. Please state all the candidate keys of the schema Player.

Answer 1

1. NON-Trivial Functional Dependency

If a functional dependency X -> Y holds true when Y is not a subset of X then this type of dependency is known as non-trivial dependency.

For the given schema Player the set of non-trivial functional dependency are-

ID -> Birthday, Address, Email, Phone, PlayPos

Name -> Birthday, Address, Email, Phone, PlayPos

Email -> ID, Name

Phone -> ID, Name

ID -> Name

Name -> ID

In each of given above functional dependency Y is not a sub set of X.

2.

A candidate key is a set of column in a relation which uniquely identifies a record in a table without referring to the other attributes. A table may have one or more candidate key. It is a minimal set of attributes necessary to identify a tuple in a relation.

In the given relation Player the attribute ID and Name both can uniquely identify a tuple, so the candidate key for relation Player would be-

{ID}

{Name}