29-01-2013, 04:48 PM
Functional Dependencies and Normalization
Functional Dependencies.ppt (Size: 1.27 MB / Downloads: 22)
Introduction
The idea is to find a methodology to choose the good relation schemas among many proposed schemas.
We are interested here in measuring the “goodness” at the conceptual level (logical level). So, the users can understand their meaning of the data clearly, and hence they can formulate their queries correctly.
Topic Roadmap
Determine some informal criteria for getting good relation schemas.
Functional Dependencies, as a tool to measure the appropriateness of attributes grouping into relation schemas.
The process of Normalization.
Informal Design Guidelines
There are four informal measures of quality for relation schema design:
Semantics of Relation Attributes:
It is assumed that there exists a meaning associated with grouping certain attributes in a relation schema.
The grouping of some attributes in a relation schema must be done in a way to make the understanding of the attributes and their relations is clear.
Functional Dependencies
A Functional Dependency is a constraint between two sets of attributes from the database.
A Functional Dependency is a property of the semantics of the attributes and not of a particular legal relation state r of R.
The designers use their understanding to specify the Function Dependencies (FDs) that should hold on all relation states.
Inference Rules for FDs
The set of FDs specified on R is denoted by F.
Many other FDs can be inferred from F.
The set of all such FDs inferred from F is denoted by F+ (closure of F).
Normalization
Normalization is the process of taking a relation schema through a series of tests to certify whether it satisfies a certain normal form (certain conditions).
The process proceeds in a top-down way by evaluating each relation against the criteria for normal forms and decomposing the relation as necessary.
The process was initially proposed by Codd (1972) and he proposed three normal forms (1NF, 2NF and 3NF), then he proposed a stronger normal form which is BCNF.