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Multivalued Dependency and Fourth Normal Form


Normalization is the essential concept of data management which is used to organize the information in relational databases efficiently and effectively to reduce the redundancy in the information. This mainly entails structuring and optimizing data attributes in a data base to cut out data redundancy and enhance simple and orderly storage. The Fourth Normal Form (4NF), one of the normalization levels, helps to deal with the more specific types of redundancy related to multivalued dependencies.

Multivalued Dependency and Fourth Normal Form

Understanding Multivalued Dependencies (MVD)

Multivalued dependencies on the other hand are also a form of database constraints but of more complexity than the functional ones. A multivalued dependency in relation database environment is defined as one or more attributes of a table deciding other attributes in the same table but with regards to other attributes in the table. This entails that for a certain instance of one attribute, there could be distinct values of another attribute that are independent of each other.

Examples of Multivalued Dependencies in Databases:

Consider a table representing a bookstore's inventory:

Multivalued Dependency and Fourth Normal Form

They are both examples of multivalued dependencies between the relation elements of Book and Author and between Book and Genre. Unlike authors and genres, where multiple generically absolute entries may correspond to one identically-name book.

How MVDs Differ from Functional Dependencies:

This means that functional dependencies are those that encompass only one mapping whereby one attribute is determinative of another. For example, in a table of employees, each value of EmployeeID potentiality belongs to only one value of EmployeeName. As the case may be, multivalued dependencies can hold more than two associations that are independent of each other. As indicated MVD"s are responsible for redundancy, it is therefore important to understand this distinction.

Identifying Multivalued Dependencies

Multivalued dependencies in a database schema are the checked and determined in the identification of one or more attributes where one attribute depends on one or more values of other attributes.

Rules and Conditions for Multivalued Dependencies:

Multivalued dependencies in a table are represented by the notation X →→ Y, indicating that if two rows are identical in their values in the column X, then their Y values are inconsequential of Z values (where Z is any attribute set in the table).

Techniques for Detecting MVDs in Database Schemas:

Data Analysis: To explore the contingency of attributes to investigate the opportunities where some of the attributes change while others remain stable.

Schema Review: Determining in tables, the feasibility of multivalued dependency based on attributes of the table.

Dependency Diagrams: The utilization diagrams for subsequent analysis helps in determining the dependencies and the Most Valuable Dependencies.

Fourth Normal Form (4NF)

Fourth Normal Form (4NF) is the forth level of normalization, with the purpose of eliminating multivalued dependency and the redundancy that comes with it. A table is said to be in 4NF if it correspond to Boyce Codd Normal Form (BCNF) and free from non trivial Multivalued dependency.

Differences Between Third Normal Form (3NF) and Fourth Normal Form (4NF):

  • 3NF: Every table that is in the third normal form is also in the second normal form, and, all the attributes in the table are fully determined by the primary key attribute.
  • 4NF: It is defined in terms of a frame of reference and keeps stored in a computer database, for example as a row in a table in relational database that is in 3NF (more precisely BCNF) and containing no non-trivial multivalued dependencies.

Achieving Fourth Normal Form

A process of attaining 4NF prevents tables with MVDs to include redundant details that require decomposition into other smaller tables.

Steps to Normalize a Database to 4NF:

Identify Multivalued Dependencies: Identify the current state MVDs of the schema under consideration.

Decompose Tables: Save MVDs in different tables by creating new tables and making sure that each MVD is not influenced by other tables.

Reorganize Data: Perform one last modification of the schema in order to avoid any data duplication in the database.

Example of 4NF:

Considering a table:

Multivalued Dependency and Fourth Normal Form

Multiple values depend on this table: This means that NameForArtist and Genre are two independent notions defined in relation to the common parameter - AlbumID.

Decomposed into 4NF:

Multivalued Dependency and Fourth Normal Form
Multivalued Dependency and Fourth Normal Form

When decomposing, we have the opportunity to take away the multi valued dependencies and this leads to the achieving of the 4NF. They help reduce the redundancy of information as well as organising information logically all in one structure.

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