How do you find the candidate key for functional dependency?
The candidate key can be determined from given set of functional dependency in a relation. It is an attribute or minimal set of attributes whose closure is set of all attributes in a relation. = ABCD. Find the candidate keys in above relation.
What are the candidate keys of R?
Candidate Key is a Super Key whose no proper subset is a super key, i.e. suppose if ABC is a candidate key then neither A, B, C or any of its combination can be super key, hence we can say candidate key is a minimal set of attributes of an R( Relational Schema) which can be used to identify a tuple of a table uniquely.
Are Keys functional dependencies?
Each component of a composite key is known as a Key Attribute. When an attribute is functionally dependent on an entire composite key, and not just on parts of the composite key, then it is said to be fully functionally dependent.
What is the use of candidate key?
A candidate key is a specific type of field in a relational database that can identify each unique record independently of any other data. Experts describe a candidate key of having “no redundant attributes” and being a “minimal representation of a tuple” in a relational database table.
How are candidate keys related to functional dependencies?
If you have all attributes you have a superkey. eg: ACD is a superkey because I have ABCDE. CD is the candidate key, so ACD, BCD, CDE all can be candidate key. C,D do not appear in the right side of any functional dependencies which is why CD is candidate key.
What are the attributes of a candidate key?
A candidate key is a minimal superkey. In other words, there are no superflous attributes in the key. The first step to finding a candidate key, is to find all the superkeys. For those unfamiliar, a super key is a set of attributes whose closure is the set of all atributes.
Can a candidate key be a Super key?
Note: A candidate key is always a super key but vice versa is not true. Q. Finding Candidate Keys and Super Keys of a Relation using FD set The set of attributes whose attribute closure is set of all attributes of relation is called super key of relation. For Example, the EMPLOYEE relation shown in Table 1 has following FD set.
How to find the candidate key for a sub relation?
{CD}+ = C D A, cant derive all the attributes present in the sub relation i.e BCD, so its not a candidate key. {BCD}+ =, Not possible, since it’ll become the super key of BD. Therefore, BD hast= the capacity to uniquely derive all the attributes present in the sub relation i.e BCD. Therefore BD is the candidate key.