Concepts of Database Management, Fifth Edition Chapter 5: Database Design 1: Normalization

Concepts of Database Concepts of Database Management, Fifth Management, Fifth

EditionEdition

Chapter 5: Chapter 5:

Database Design 1:Database Design 1:

NormalizationNormalization

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Concepts of Database Management

Objectives

Discuss functional dependence

Discuss primary keys

Define first normal form, second normal form, and third normal form

Describe the problems associated with tables (relations) that are not in first normal form, second normal form, or third normal form along with the mechanism for converting to all three

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Objectives

Discuss the problems associated with incorrect conversions to third normal form

Define fourth normal form

Describe the problems associated with tables (relations) that are not in fourth normal form and describe the mechanism for converting to fourth normal form

Understand how normalization is used in the database design process

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Normalization

Normalization process – enables you to identify the existence of potential problems, called updating anomalies, in the design of a relational database

Normal form – possesses a certain desirable collection of properties

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Figure 5.1:Premiere Products Data

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Functional Dependence

Column B is functionally dependent on Column A if A’s value determines a single value for B at a given time

Given A, a single value for B can be determined

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Functional Dependence

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Figures 5.3-5.4:Functional Dependence Example

Rep Table Where LastName can determine record

Rep Table Where LastName cannot determine record

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Keys Column(s) C is primary key for table T if:

Property 1: All columns in T are functionally dependent on C

Property 2: No subcollection of columns in C (assuming C is a collection of columns and not just a single column) also has Property 1

Candidate Keys Column(s) on which all other columns in table are

functionally dependent

Alternate Keys Candidate keys not chosen as primary keys

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First Normal Form (1NF)

Unnormalized table

Contains a repeating group

Table in 1NF

Contains no repeating groups

Removal of repeating groups is starting point in quest for problem-free tables

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Figure 5.5: 1NF Example

Unnormalized Table

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Figure 5.6: 1NF Example (con’t.)

Conversion to 1NF

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Second Normal Form (2NF)

1NF Tables may contain problems Redundancy

Update Anomalies Update, inconsistent data, additions, deletions

Occur because a column is dependent on a portion of a multi-column primary key

2NF Table In 1NF and no nonkey column is dependent on

only a portion of the primary key

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Figure 5.7:Second Normal Form

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Update Anomalies Update

Information is in multiple rows, difficult to update

Inconsistent data Because of the duplication, a row that is not updated

causes inconsistency

Additions Dummy records are required to add new unused

dependent rows

Deletions Nonkey column (nonkey attribute) – when a

column is not a part of the primary key

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Dependency Diagram

Dependency diagram – uses arrows to indicate all the functional dependencies present in a table

Partial dependencies – dependencies only on a portion of the primary key

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Figure 5.8:Dependency Diagram for Orders

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Third Normal Form (3NF)

2NF Tables may still contain problems Redundancy and wasted space

Update Anomalies Update, inconsistent data, additions, deletions

Occur because a column is dependent on a portion of a multi-column primary key

3NF Table In 2NF and the only determinants contained are

candidate keys

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Figure 5.10: Sample Customer Data

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Figure 5.11:Customers Dependency Diagram

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Incorrect Decomposition

Decomposition must take place according to that described for 3NF

Even though you may decompose a table, you run the risk of splitting the functional dependence across different tables

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Figure 5.13: Incorrect Decomposition Example

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Fourth Normal Form (4NF)

3NF Tables may still contain problems

Dependencies

Update Anomalies

Update, additions, deletions

Occur because of multivalued dependencies

4NF Table

In 3NF and has no multivalued dependencies

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Figure 5.15: Incorrect 4NF Example

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Figure 5.16a: 4NF Example

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Figure 5.17: Normal Forms

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Summary

Normalization is a process of optimizing databases to prevent update anomalies

Normalization attempts to correct update issues by eliminating duplication

Duplication also creates inconsistency

Insertions can violate database integrity if the database is not normalized

Deletions can violate database integrity if the database is not normalized

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Summary (con’t.)

Normal Forms – First (1NF), Second (2NF), Third(3NF), and Fourth(4NF)

1NF has no repeating groups

2NF is in 1NF and no non-key column is dependent on only a portion of the primary key

3NF is in 2NF and the only determinants are candidate keys

4NF is in 3NF and has no multivalued dependencies

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Concepts of Database Management, Fifth Edition Chapter 5: Database Design 1: Normalization