An electromagnetic pulse (EMP) is a short burst of electromagnetic energy interference caused by an abrupt and rapid acceleration of charged particles, which can damage electronic components by short-circuiting them. An EMP can contain many energy components of the electromagnetic spectrum, from the very low frequency waves to the ultraviolet...
Functional dependency is a relationship that exists when one attribute uniquely determines another attribute.
If R is a relation with attributes X and Y, a functional dependency between the attributes is represented as X->Y, which specifies Y is functionally dependent on X. Here X is a determinant set and Y is a dependent attribute. Each value of X is associated precisely with one Y value.
Functional dependency in a database serves as a constraint between two sets of attributes. Defining functional dependency is an important part of relational database design and contributes to aspect normalization.
A functional dependency is trivial if Y is a subset of X. In a table with attributes of employee name and Social Security number (SSN), employee name is functionally dependent on SSN because the SSN is unique for individual names. An SSN identifies the employee specifically, but an employee name cannot distinguish the SSN because more than one employee could have the same name.
Functional dependency defines Boyce-Codd normal form and third normal form. This preserves dependency between attributes, eliminating the repetition of information. Functional dependency is related to a candidate key, which uniquely identifies a tuple and determines the value of all other attributes in the relation. In some cases, functionally dependent sets are irreducible if:
An important property of a functional dependency is Armstrong’s axiom, which is used in database normalization. In a relation, R, with three attributes (X, Y, Z) Armstrong’s axiom holds strong if the following conditions are satisfied:
Read More »
Join 138,000+ IT pros on our weekly newsletter
Home | Advertising Info | Write for Us | About | Contact Us
2010 - 2015
Partner Sites :