Explain functional and transitive dependency.

Functional Dependency: 

A functional dependency occurs when one attribute in a relation uniquely determine another attribute.  

OR 

Let ‘R’ be a relation and let X and Y be any arbitrary attributes of R, then it can be said that Y is functionally dependent on X if and only if, each X value is associated with precisely one Y value. And it can be shown as X→ Y. e.g. emp_id →ename meaning ename functionally dependent on emp_id. 

Transitive Dependency:

A Functional dependency is said to be transitive if it is indirectly formed by two functional dependencies. The Transitive dependency exist between X → Z if the following three Functional dependencies hold true. 

1.X → Y

2.Y does not → X

3. Y → Z then

X → Z 

The Transitive Dependency can only occur in a relation which has three or more attributes. This dependency needs to be eliminated to make relation in 3NF. 

OR 

If we have a primary key A and a non-key domain B and C, where C is more dependent on B than A; and B is directly dependent on A, then C can be considered transitively dependent on A. 

Example:

Consider the relation SUPPLIER (SNO, SNAME, CITY, STATUS).  

In this dependency STATUS is dependent on CITY and CITY is functionally dependent on SNO, which shows a transitive dependency i.e. STATUS is transitively depending on SNO(i.e. via CITY).