DBMS NORMALISATION PDF

For example, there are discussions even on 6th Normal Form. The evolution of Normalization theories is illustrated below- Database Normalization Example: We will study normalization with the help of a case study. Assume, a video library maintains a database of movies rented out. Without any normalization, all information is stored in one table as shown below. Here you see Movies Rented column has multiple values. Each record needs to be unique.

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So, it is a superkey. Consider the combination of columns course code, professor name. It is also unique across various rows. So, it is also a superkey. A superkey is basically a set of columns such that the value of that set of columns is unique across various rows. That is, no 2 rows have the same set of values for those columns.

Some of the superkeys for the table above are: Course code Course code, professor name Course code, professor mobile number A superkey whose size number of columns is the smallest is called as a candidate key.

For instance, the first superkey above has just 1 column. The second one and the last one have 2 columns. So, the first superkey Course code is a candidate key. A trivial functional dependency means that all columns of B are contained in the columns of A. Basically, if a set of columns B can be determined knowing some other set of columns A , then A should be a superkey. Superkey basically determines each row uniquely. It is a trivial functional dependency: this means that there should be no non-trivial dependency.

This may lead to an inconsistent database. There are also 2 other normal forms: Fourth normal form A table is said to be in fourth normal form if there is no two or more, independent and multivalued data describing the relevant entity. Fifth normal form A table is in fifth Normal Form if: It is in fourth normal form.

It cannot be subdivided into any smaller tables without losing some form of information. Summary The various forms of database normalization are useful while designing the schema of a database in such a way that there is no data replication which may possibly lead to inconsistencies.

While designing the schema for applications, we should always think about how can we make use of these forms. People are also reading:.

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Normalization in DBMS: 1NF, 2NF, 3NF and BCNF with Examples

Next Page Functional Dependency Functional dependency FD is a set of constraints between two attributes in a relation. Functional dependency says that if two tuples have same values for attributes A1, A2, The left-hand side attributes determine the values of attributes on the right-hand side. That is adding attributes in dependencies, does not change the basic dependencies. Trivial FDs always hold. Normalization If a database design is not perfect, it may contain anomalies, which are like a bad dream for any database administrator.

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Database normalization

Prerequisite — Database normalization and functional dependency concept. Normalization is the process of minimizing redundancy from a relation or set of relations. Redundancy in relation may cause insertion, deletion and updation anomalies. So, it helps to minimize the redundancy in relations.

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