Prerequisite — Functional Dependency , Database Normalization , Normal Forms If two or more independent relation are kept in a single relation or we can say multivalue dependency occurs when the presence of one or more rows in a table implies the presence of one or more other rows in that same table. Put another way, two attributes or columns in a table are independent of one another, but both depend on a third attribute. A multivalued dependency always requires at least three attributes because it consists of at least two attributes that are dependent on a third. For example,.
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Prerequisite — 4th and 5th Normal form. Fourth Normal Form 4NF : Any relation is said to be in the fourth normal form when it satisfies the following conditions:. A multi-valued dependency is said to occur when there are two attributes in a table which depend on a third attribute but are independent of each other. Thus if a relation is in BCNF and also it does not have any kind of multi-valued dependency then that relation will be in 4NF. In this relation Student-ID 1 has thus opted for two courses and has two hobbies.
Similarly Student-ID 2 has opted for two courses and has two hobbies. Thus it contains multi-valued dependencies. It is not in 4NF and in order to convert it into 4NF it can be decomposed into two relations:. Now this relation is thus in 4NF. A relation can contain a functional dependency along with a multi-valued dependency also. So when such a case arises the columns which are functionally dependent are moved to a separate table and the columns which are multi-valued dependent are moved to a separate table.
This converts the relation into 4NF. Fifth Normal Form 5NF : Any relation in order to be in the fifth normal form must satisfy the following conditions:. In the fifth normal form the relation must be decomposed in as many sub-relations as possible so as to avoid any kind of redundancy and there must be no extra tuples generated when the sub-relations are combined together by using natural join.
A relation in 5NF cannot be decomposed further without any kind of modification in the meaning or facts. Thus if natural join is performed on all the three relations then there will be no extra tuples. GeeksforGeeks has prepared a complete interview preparation course with premium videos, theory, practice problems, TA support and many more features.
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Load Comments. If a relation is in Fifth Normal Form then it cannot be decomposed further into sub-relations without any modification in meaning or facts.
BCNF, 4NF and 5NF
Fifth normal form (5NF)