Functional Dependency

Topics: Database normalization, Denormalization, Social Security number Pages: 1 (447 words) Published: October 22, 2014

Functional Dependency
Functional Dependency is the starting point for the process of normalization. Functional dependency exists when a relationship between two attributes allows you to uniquely determine the corresponding attribute’s value. If ‘X’ is known, and as a result you are able to uniquely identify ‘Y’, there is functional dependency. Combined with keys, normal forms are defined for relations.

Examples
Bear Number determines Student Name:
BearNum ---> StuName
Department Number and Job Rank determine Security Clearance: (DeptNum, JRank) --->SecClear
Social Security Number determines Employee Name and Salary: SSN ---> (EmpName, Salary)
Additionally, the above can be read as:
SSN --->EmpName and SSN Salary
Transitive dependencies occur when there is an indirect relationship that causes a functional dependency. For more detail, read What is a Database Dependency?
Examples: For example, ”A -> C” is a transitive dependency when it is true only because both “A -> B” and “B -> C” are true. Definition - What does Denormalization mean?
Denormalization is a strategy that database managers use to increase the performance of a database infrastructure. It involves adding redundant data to a normalized database to reduce certain types of problems with database queries that combine data from various tables into a single table. The definition of denormalization is dependent on the definition of normalization, which is defined as the process of organizing a database into tables correctly to promote a given use. In many cases, denormalization involves creating separate tables or structures so that queries on one piece of information will not affect any other information tied to it. For instance, where more global data variables such as customer names are tied together with single purchases in a purchase history, a database administrator will want to make sure that work done on an item purchased will not incorrectly affect the...
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