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Dipankar

A relation is in 3NF if it is in 2NF (no partial dependency on key) and there is no Transitive dependencies. A relation to be in 3NF if for every non-trival FDs of the form A->B either A is a key or B is a prime (attribute forming up the composite key) attribute. when decomposing a relation to 3NF we consider the FDs where a non-key attribute functionally determines another non-key attribute. BCNF is strict say for every non-trival FDs of the form A->B A(determinant) should be the key. Thus BCNF do not allow a non-key attribute to functionally determine a prime(part of key) attribute, which is relaxed in 3NF. A relation R which is in 3NF is not in BCNF only if there exists composite overlapping keys and a non-overlapping attribute functionally determines another non-overlapping attribute. However, a relation which is in BCNF satisfy to be allways in 3NF. 4NF considers regarding non-trival multivalued functional dependency. 5NF(PJNF) considers regarding join-dependency. for better understanding we consider the relational state (extension) of the Relation R. for a relation having non-trival multivalued dependency, it has 3 or more attributes, on a relation schema R. based on MVD X->>Y , we decompose R into R1=(X U Y) and R2=(R-Y). Observing r(R) we may find no two or more independent MVDs, however it may suffer from the database anamolies, which is dealt with in PJNF. We consider the nonadditive join decomposition in 5NF. So, a Relation having 3 attributes may be decomposed into 3 relations such that lossless decomposition can be achieved. The Domain Key Normal Form is said to be the ultimate Normal Form and might be usefull in designing distributed database systems. DKNF enforces database constraints by checking that each attribute in a tuple is of the appropriate domain and the key constraints are enforced.