Page 149 - DCAP402_DCAO204_DATABASE MANAGEMENT SYSTEM_MANAGING DATABASE

Database Management Systems/Managing Database

Notes columns into separate tables along with a copy of the determinant. This copy serves as a foreign
key to the original table.

Table before Fourth Normal Form

Branch_Staff Table
BranchNumber StaffName ClientName
B-41 Radha Surya
B-41 Radha Ravi
B-41 Smitha Surya
B-41 Smitha Ravi

Table after Fourth Normal Form

Branchjitaff Table

BranchNumber ClientName BranchNumber StaffName
B-41 Surya B-41 Radha
B-41 Ravi B-41 Smitha

Task BCNF differ from 4 NF. Explain.
th
8.7 Fifth Normal Form

The Fifth Normal form is usually applied only for large relational data models. The Fifth
Normal form states that the original table must be reconstructed from the tables into which it
has been decomposed. 5NF allows decomposing a relation into three or more relations. Fagin
defined the 5NF and according to Fagin’s theorem, a relation (A, B, C) can be decomposed
lossless in (A, B) and (A, C) if and only if A B|C is true in (A, B, C).

The fifth normal form is based on the concept of join dependency. Join dependency means that
a table, after it has been decomposed into three or more smaller tables, must be capable of being
joined again on common keys to form the original table. The join dependency is more general
form of multi-valued dependency.
A relation R satisfies join dependency (R , R …. R ) if and only if R is equal to the join of
1 2 n
R , R …. R where R are subsets of the set of attributes of R.
1 2 n i
A relation R is in 5NF (or project-join normal form, PJNF) if for all join dependencies at least one
of the following holds.
1. (R , R …. R ) is a trivial join-dependency (that is, one of R is R)
1 2 n t
2. Every R is a candidate key for R.
i

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