Normalization Essay

1733 words - 7 pages

Normalization of Database Tables
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Introduction to Normalization of Database Tables

Normalization of Database Tables
ISM 602 Dr. Hamid Nemati

Introduction to Normalization of Database Tables

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Objectives The idea of Dependencies of Attributes Normalization and Database Design Understand concepts of normalization (Higher-Level Normal Forms) Learn how to normalize tables Understand normalization and database design issues Denomalization

Functional Dependency
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Introduction to Normalization of Database Tables

Examples of Functional Dependencies:
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Introduction to Normalization of Database Tables

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A Functional Dependency Is A Relationship Between ...view middle of the document...

Goals Of Normalization:
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Eliminate Redundancies Caused By:
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EMPLOYEE_ID --> JOB_CATEGORY JOB_CATEGORY --> HOURLY_RATE
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Fields Repeated Within A File Fields Not Directly Describing The Key Entity Fields Derived From Other Fields

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An employee data table that includes the “hourly pay rate” would require searching every employee record to properly update an hourly rate for a particular job category.

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Avoid Anomalies In Updating (Adding, Editing, Deleting) Represent Accurately The Items Being Modeled Simplify Maintenance And Retrieval Of Info

Database Tables and Normalization
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Introduction to Normalization of Database Tables

Basic Rule for Normalization
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Introduction to Normalization of Database Tables

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Normalization is a process for assigning attributes to entities. It reduces data redundancies and helps eliminate the data anomalies. Normalization works through a series of stages called normal forms:
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The attribute values in a relational table should be functionally dependent (FD) on the primary key value.
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First normal form (1NF) Second normal form (2NF) Third normal form (3NF)

A relationship is functionally dependent when one attribute value implies or determines the attribute value for the other attribute.
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EM_SS_NUM --> EM_NAME

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Corollaries
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The highest level of normalization is not always desirable.

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Corollary 1: No repeating groups allowed in relational tables. Corollary 2: A relational table should not have attributes involved in a transitive dependency relationship with the primary key.

Normalization Benefits
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Introduction to Normalization of Database Tables

Database Tables and Normalization
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Introduction to Normalization of Database Tables

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Facilitates data integration. Reduces data redundancy. Provides a robust architecture for retrieving and maintaining data. Compliments data modeling. Reduces the chances of data anomalies occurring.

The Need for Normalization
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Case of a Construction Company
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Building project -- Project number, Name, Employees assigned to the project. Employee -- Employee number, Name, Job classification The company charges its clients by billing the hours spent on each project. The hourly billing rate is dependent on the employee’s position.

Database Tables and Normalization
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Introduction to Normalization of Database Tables

Deletion Anomaly
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Introduction to Normalization of Database Tables

Problems with the Table 5.1
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The project number is intended to be a primary key, but it contains nulls. The table displays data redundancies. The table entries invite data inconsistencies. The data redundancies yield the following anomalies:
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Occurs when the removal of a record results in a loss of important information about an entity. Example:
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All the information about a customer is contained in an order file, if the order is...

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