Research Work

o Database Normalization

Definition

It is the process of organizing data in a database. This includes creating tables and establishing relationships between those tables according to rules designed both to protect the data and to make the database more flexible by eliminating redundancy and inconsistent dependency. 

History

Normalization was developed by an IBM researcher named E.F. Codd in the early 1970s; he also invented the relational database.

Importance

It serves to remove duplication from the database records.

For example if you have more than one place (tables) where the name of a person could come up you move the name to a separate table and reference it everywhere else. This way if you need to change the person name later you only have to change it in one place.

It highlights constraints and dependency in the data and hence aid the understanding the nature of the data

Normalization controls data redundancy to reduce storage requirement and standard maintenance

Normalization provide unique identification for records in a database Each stage of normalization process eliminate a particular type of

undesirable dependency Normalization permits simple data retrieval in response to reports and

queries The third normalization form produces well designed database which

provides a higher degree of independency Normalization helps define efficient data structures Normalized data structures are used for file and database design Normalization eliminate unnecessary dependency relationship within a

database file

Stages of Normal Forms

1. First Normal Form Eliminate repeating groups in individuals. Create a separate table for each set related data. Identify each set of related data with a primary key.

Refers to the first step where preliminary data structures are transforming into the first normal form by eliminating any repeating sets of data elements. A relation table is said to be on the first normal form, if and only if it contains no repeating groups that is it has no repeated value for a particular attribute with a single record. Any repeated group of attribute is isolated to form a new relation. In other words first normal form (1nf) means that a table has no multiple value attribute or composite attribute, In the 1nf, each column holds one attribute and each row holds a single occurrence of the entity.

Tables should have only two dimensions. Since one student has several classes, these classes should be listed in a separate table. Fields Class1, Class2, and Class3 in the above records are indications of design trouble.

Spreadsheets often use the third dimension, but tables should not. Another way to look at this problem is with a one-to-many relationship, do not put the one side and the many side in the same table. Instead, create another table in first normal form by eliminating the repeating group (Class#), as shown below:

Stud# Advisor Adv- Room Class#1022 Jones 412 101-071022 Jones 412 143-011022 Jones 412 159-024123 Smith 216 201-014123 Smith 216 211-024123 Smith 216 214-01

2. Second Normal Form Create separate tables for sets of values that apply to multiply

records. Relate these tables with a foreign key.

2nf concentrated on records with concatenated keys, they check the non key attribute for dependency on the entire key, and any data element that dependent only on part of the key is moved to a new entity.

Note the multiple Class# values for each Student# value in the above table. Class# is not functionally dependent on Student# (primary key), so this relationship is not in second normal form.

The following two tables demonstrate second normal form:

Students:

Student# Advisor Adv-Room1022 Jones 412

4123 Smith 216

Registration:

Student# Class#1022 101-071022 143-011022 159-024123 201-014123 211-024123 211-01

3. Third Normal Form Eliminate fields that do not depend on the key.

All data element in the third normal form must be a function of the key. To reach the 3nf, you need to review the structure’s non-key data elements and identify any data element dependent on an attribute other than the key, if there is all these data elements should be moved to a new entity

Adv-Room (the advisor's office number) is functionally dependent on the Advisor attribute. The solution is to move that attribute from the Students table to the Faculty table, as shown below:

Student:

Stud# Advisor1022 Jones4123 Smith

Faculty:

Name Room DeptJones 412 42Smith 216 42

4. Fourth Normal Form

It deals with data element with issues of multi-value dependency (when one attributes determine another attribute sets). A relation is said to be in the 4nf formal form if and if only all existing multi-value dependency is converted into functional dependency.

CourseId Instructor TextbookMGS404 Clay HansenMGS404 Clay KroenkeMGS404 Drake HansenMGS404 Drake Kroenke

By placing the multivalued attributes I tables by themselves, we can convert the above to 4NF.

Change to: COURSE-INST(Course-Id, Instructor)COURSE-TEXT(Course-Id, Textbook)

5. Fifth Normal Form

Where the join dependency is removed, the 5nf is also known as the projection join normal form(PJNF), and refers to the separation of one relation into any sub-relations or having sub-relations into one relation and can produce join dependencies.

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