A functional dependency is defined as a constraint between two sets of attributes in a relation from a database. Chapter 11 functional dependencies database design 2nd. A functional dependency is a type of constraint that is a generalization of the notion of key, as discussed in chapters 2 and 3. Pdf a software tool to transform relational databases in. Given a relation r, a set of attributes x in r is said to functionally determine. Functional dependency defines boycecodd normal form and third normal form.
Defining functional dependency is an important part of relational database design and contributes to aspect normalization. Functional dependency in dbms, as the name suggests is a relationship between attributes of a table dependent on each other. It typically exists between the primary key and nonkey attribute within a table. A functional dependency fd is a relationship between two attributes, typically.
This paper shows, that functional dependency theory provides a. The attributes of a table is said to be dependent on each other when an attribute of a. A functional dependency x y is said to be trivial if and only if y. This situation is not desirable because a nonkey attribute programname. Thus, if rhs of a functional dependency is a subset of lhs, then it is called as a trivial functional dependency. Functional dependencies play a key role in differentiating good database designs from bad database designs.
Functional dependency is related to a candidate key, which uniquely identifies a tuple and determines the value of all other attributes in the relation. In other words, a functional dependency is a constraint between two keys. In relational database theory, a functional dependency is a constraint between two sets of attributes in a relation from a database. Database management system multiple choice questions and answers or dbms mcqs for gate, net exam from chapter functional dependencies. Functional dependency and attribute closure geeksforgeeks. The application of functional dependency theory to relational. Codd, it helps in preventing data redundancy and gets to know about bad designs. The problem is to find all possible functional dependencies among attributes in a relational database 1. We assume that a relational database consists of a set of relations. Functional dependencies are constraints on the set of legal relations.
Learn more about database functional dependency based on relational databases and the importance of database management systems. This preserves dependency between attributes, eliminating the repetition of information. The left side of fd is known as a determinant, the right side of the production is known as a dependent. Functional dependency helps you to maintain the quality of data in the database. A software tool to transform relational databases in order to mine functional dependencies in it using formal concept analysis conference paper pdf available october 2008 with 184 reads. The previous for discovering functional dependencies is based on repeated sorting and comparing of tuples to determine whether or not these tuples meet fd definition. These solved objective questions with answers for online exam preparations section include dependency preservation. Functional dependency questions and answers database. Functional dependencies fd in the relational database management system occurs when one attribute in a relation uniquely determines. The functional dependency is a relationship that exists between two attributes. Functional dependency fd determines the relation of one attribute to another attribute in a database management system dbms system.