22-01-2013, 04:32 PM
Database Normalization
1Database Normalization.docx (Size: 31.12 KB / Downloads: 27)
Forms of Database
Database normalization is the process of organizing the fields and tables of a relational database to minimize redundancy and dependency.
Normalization usually involves dividing large tables into smaller (and less redundant) tables and defining relationships between them. The objective is to isolate data so that additions, deletions, and modifications of a field can be made in just one table and then propagated through the rest of the database via the defined relationships.
Edgar F. Codd, the inventor of the relational model, introduced the concept of normalization and what we now know as the First Normal Form (1NF) in 1970.[1] Codd went on to define the Second Normal Form (2NF) and Third Normal Form (3NF) in 1971,[2] and Codd and Raymond F. Boyce defined the Boyce-Codd Normal Form (BCNF) in 1974.[3]Informally, a relational database table is often described as "normalized" if it is in the Third Normal Form.[4] Most 3NF tables are free of insertion, update, and deletion anomalies.
Background of Normalization
Functional dependency
In a given table, an attribute Y is said to have a functional dependency on a set of attributes X (written X → Y) if and only if each X value is associated with precisely one Value. For example, in an "Employee" table that includes the attributes "Employee ID" and "Employee Date of Birth", the functional dependency .
Database Structure
A Microsoft Access database is a single file with the file extension *.mdb and is often referred to as
a database application since, unlike other Microsoft Office files it can contain many different objects
and work as if it were a program in its own right. Usually you need a copy of Microsoft Access to
run an Access database, although Access developers (programmers) can create and distribute
Access databases that will work completely independently of the Microsoft Access program so that
the user does not need a separate copy of Access to run the database. These are known as runtime
databases.
Access database files are also different from other Microsoft Office files (such as Excel Workbooks)
in that they permit more than one user to work with the file simultaneously. An Access database
can have up to 255 concurrent users.
Database Objects
An Access database can consist of many different components. These are called the database
objects. They are organised into groups according to type and are listed in the Access database
window which is normally displayed when the database opens.
Tables
Tables are the most important part of a database. They contain the data. Tables present the data
as a datasheet with the data arranged in rows (records) and columns (fields) (Fig. 2). You can edit
data directly in a table and add or delete records. The data can also be sorted and filtered in this
view. Data in a table can be selected, copied and pasted into another application or exported as a
file. An Access table can have up to 255 fields and can contain up to 2 million records.