DBMS 面试题与答案

A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully functionally dependent on primary key.

A relation schema R is in 3NF if it is in 2NF and for every FD X A either of the following is true 

1. X is a Super-key of R. 

2. A is a prime attribute of R. 

In other words, if every non prime attribute is non-transitively dependent on primary key. 

A relation schema R is in BCNF if it is in 3NF and satisfies an additional constraint that for every FD X A, X must be a candidate key.

A relation schema R is said to be in 4NF if for every Multivalued dependency X Y that holds over R, one of following is true. 

1.) X is subset or equal to (or) XY = R. 

2.) X is a super key. 

A Relation schema R is said to be 5NF if for every join dependency {R1, R2, ..., Rn} that holds R, one the following is true 

1) Ri = R for some i. 

2) The join dependency is implied by the set of FD, over R in which the left side is key of R.