Chapter 7 Logical Database Design Fundamentals of Database Management Systems by Mark L. Gillenson, Ph.D. University of Memphis Presentation by: Amita

Chapter 7Chapter 7Logical Database Logical Database

DesignDesign

Fundamentals of Database Management Systemsby

Mark L. Gillenson, Ph.D.

University of Memphis

Presentation by: Amita Goyal Chin, Ph.D.

Virginia Commonwealth University

John Wiley & Sons, Inc.

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Chapter ObjectivesChapter Objectives

Describe the concept of logical database Describe the concept of logical database design. design.

Design relational databases by converting Design relational databases by converting entity-relationship diagrams into relational entity-relationship diagrams into relational tables. tables.

Describe the data normalization process.Describe the data normalization process.

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Chapter ObjectivesChapter Objectives

Perform the data normalization process. Perform the data normalization process.

Test tables for irregularities using the data Test tables for irregularities using the data normalization process. normalization process.

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Logical Database DesignLogical Database Design

The process of deciding how to arrange The process of deciding how to arrange the attributes of the entities in the business the attributes of the entities in the business environment into database structures, environment into database structures, such as the tables of a relational such as the tables of a relational database.database.

The goal is to create well structured tables The goal is to create well structured tables that properly reflect the company’s that properly reflect the company’s business environment.business environment.

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Logical Design of Relational Logical Design of Relational Database SystemsDatabase Systems

(1) The conversion of E-R diagrams into (1) The conversion of E-R diagrams into relational tables.relational tables.

(2) The data normalization technique.(2) The data normalization technique.

(3) The use of the data normalization (3) The use of the data normalization technique to test the tables resulting from technique to test the tables resulting from the E-R diagram conversions. the E-R diagram conversions.

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Converting E-R Diagrams into Converting E-R Diagrams into Relational TablesRelational Tables

Each entity will convert to a table.Each entity will convert to a table.

Each many-to-many relationship or Each many-to-many relationship or associative entity will convert to a table.associative entity will convert to a table.

During the conversion, certain rules must During the conversion, certain rules must be followed to ensure that foreign keys be followed to ensure that foreign keys appear in their proper places in the tables.appear in their proper places in the tables.

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Converting a Simple EntityConverting a Simple Entity

The table simply contains the attributes that were The table simply contains the attributes that were specified in the entity box.specified in the entity box.

Salesperson Number is underlined to indicate that it is Salesperson Number is underlined to indicate that it is the unique identifier of the entity and the primary key of the unique identifier of the entity and the primary key of the table.the table.

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Converting Entities in Binary Converting Entities in Binary Relationships: One-to-OneRelationships: One-to-One

There are three options for designing tables to There are three options for designing tables to represent this data.represent this data.

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One-to-One: Option #1One-to-One: Option #1

SalespersonNumber

SalespersonName

CommissionPercentage

YearofHire

OfficeNumber Telephone Size

SALESPERSON/OFFICE

The two entities are The two entities are combined into one combined into one relational table.relational table.

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Separate tables for the Separate tables for the SALESPERSON and SALESPERSON and OFFICE entities, with OFFICE entities, with Office Number as a Office Number as a foreign key in the foreign key in the SALESPERSON table. SALESPERSON table.

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Separate tables for the Separate tables for the SALESPERSON and SALESPERSON and OFFICE entities, with OFFICE entities, with Salesperson Number as a Salesperson Number as a foreign key in the OFFICE foreign key in the OFFICE table. table.

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Converting Entities in Binary Converting Entities in Binary Relationships: One-to-ManyRelationships: One-to-Many

The unique identifier of the entity on the “one side” of the The unique identifier of the entity on the “one side” of the one-to-many relationship is placed as a foreign key in one-to-many relationship is placed as a foreign key in the table representing the entity on the “many side.”the table representing the entity on the “many side.”

So, the Salesperson Number attribute is placed in the So, the Salesperson Number attribute is placed in the CUSTOMER table as a foreign key.CUSTOMER table as a foreign key.

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Converting Entities in Binary Converting Entities in Binary Relationships: One-to-ManyRelationships: One-to-Many

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Converting Entities in Binary Converting Entities in Binary Relationships: Many-to-ManyRelationships: Many-to-Many

E-R diagram with the many-to-many binary E-R diagram with the many-to-many binary relationship and the equivalent diagram using an relationship and the equivalent diagram using an associative entity.associative entity.

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An E-R diagram with two entities in a many-to-An E-R diagram with two entities in a many-to-many relationship converts to three relational many relationship converts to three relational tables.tables.

Each of the two entities converts to a table with Each of the two entities converts to a table with its own attributes but with no foreign keys its own attributes but with no foreign keys (regarding this relationship).(regarding this relationship).

In addition, there must be a third “many-to-In addition, there must be a third “many-to-many” table for the many-to-many relationship.many” table for the many-to-many relationship.

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ProductNumber

ProductName Unit Price

PRODUCT

The primary key of SALE The primary key of SALE is the combination of the is the combination of the unique identifiers of the unique identifiers of the two entities in the many-to-two entities in the many-to-many relationship. many relationship. Additional attributes are Additional attributes are the intersection data.the intersection data.

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Converting Entities in Unary Converting Entities in Unary Relationships: One-to-OneRelationships: One-to-One

With only one entity type With only one entity type involved and with a one-to-involved and with a one-to-one relationship, the one relationship, the conversion requires only conversion requires only one table.one table.

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Converting Entities in Unary Converting Entities in Unary Relationships: One-to-ManyRelationships: One-to-Many

Very similar to the one-Very similar to the one-to-one unary case.to-one unary case.

SalespersonNumber

SalespersonName

CommissionPercentage Year of Hire Manager

SALESPERSON

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Converting Entities in Unary Converting Entities in Unary Relationships: Many-to-ManyRelationships: Many-to-Many

This relationship requires two tables in the This relationship requires two tables in the conversion.conversion.

The PRODUCT table has no foreign keys.The PRODUCT table has no foreign keys.

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Converting Entities in Unary Converting Entities in Unary Relationships: Many-to-ManyRelationships: Many-to-Many

A second table is created since in the conversion of a A second table is created since in the conversion of a many-to-many relationship of any degree — unary, many-to-many relationship of any degree — unary, binary, or ternary — the number of tables will be equal to binary, or ternary — the number of tables will be equal to the number of entity types (one, two, or three, the number of entity types (one, two, or three, respectively) plus one more table for the many-to-many respectively) plus one more table for the many-to-many relationship.relationship.

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Converting Entities in Converting Entities in Ternary RelationshipsTernary Relationships

The primary key of the SALE The primary key of the SALE table is the combination of table is the combination of the unique identifiers of the the unique identifiers of the three entities involved, plus three entities involved, plus the Date attribute.the Date attribute.

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Designing the General Designing the General Hardware Company DatabaseHardware Company Database

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Designing the Good Reading Designing the Good Reading Bookstores DatabaseBookstores Database

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Designing the World Music Designing the World Music Association DatabaseAssociation Database

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Designing the Lucky Designing the Lucky Rent-A-Car DatabaseRent-A-Car Database

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The Data Normalization The Data Normalization ProcessProcess

A methodology for organizing attributes A methodology for organizing attributes into tables so that redundancy among the into tables so that redundancy among the nonkey attributes is eliminated.nonkey attributes is eliminated.

The output of the data normalization The output of the data normalization process is a properly structured relational process is a properly structured relational database.database.

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The Data Normalization The Data Normalization TechniqueTechnique

Input:Input: all the attributes that must be incorporated into the all the attributes that must be incorporated into the

databasedatabase

a list of all the defining associations between the a list of all the defining associations between the attributes (i.e., the attributes (i.e., the functional dependenciesfunctional dependencies).).

• a means of expressing that the value of one particular a means of expressing that the value of one particular attribute is associated with a single, specific value of another attribute is associated with a single, specific value of another attribute.attribute.

• If we know that one of these attributes has a particular value, If we know that one of these attributes has a particular value, then the other attribute must have some other value.then the other attribute must have some other value.

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Functional DependenceFunctional Dependence

Salesperson Number is the Salesperson Number is the determinantdeterminant..

The value of Salesperson Number The value of Salesperson Number determinesdetermines the value of Salesperson Name.the value of Salesperson Name.

Salesperson Name is Salesperson Name is functionally dependentfunctionally dependent on Salesperson Number.on Salesperson Number.

Salesperson NameSalesperson Number

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General Hardware Environment: General Hardware Environment: SALESPERSON and PRODUCTSALESPERSON and PRODUCT

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Steps in the Data Steps in the Data Normalization ProcessNormalization Process

First Normal FormFirst Normal Form

Second Normal FormSecond Normal Form

Third Normal Form Third Normal Form

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The Data Normalization The Data Normalization ProcessProcess

Once the attributes are arranged in third normal form, Once the attributes are arranged in third normal form, the group of tables that they comprise is a well-the group of tables that they comprise is a well-structured relational database with no data redundancy. structured relational database with no data redundancy.

A group of tables is said to be in a particular normal form A group of tables is said to be in a particular normal form if every table in the group is in that normal form.if every table in the group is in that normal form.

The data normalization process is progressive.The data normalization process is progressive. For example, if a group of tables is in second normal form, it is For example, if a group of tables is in second normal form, it is

also in first normal form.also in first normal form.

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General Hardware Company: General Hardware Company: Unnormalized DataUnnormalized Data

Sales-personNumber Product

Number

Sales-personName Commission

Percentage

YearofHire

Depart-mentNumber Manager

NameProductName

UnitPrice Quantity

137 194402401326722

Baker 10 1995 73 Scott HammerSawPliers

17.5026.2511.50

473170688

186 16386194402176524013

Adams 15 2001 59 Lopez WrenchHammerDrillSaw

12.9517.5032.9926.25

1745252919623071

204 2176526722

Dickens 10 1998 73 Scott DrillPliers

32.9911.50

809734

361 163862176526722

Carlyle 20 2001 73 Scott WrenchDrillPliers

12.9532.9911.50

372931102738

SALESPERSON/PRODUCT Table

Records contain multivalued attributes.Records contain multivalued attributes.

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General Hardware Company: General Hardware Company: First Normal FormFirst Normal Form

The attributes under consideration have been listed in The attributes under consideration have been listed in one table, and a primary key has been established.one table, and a primary key has been established.

The number of records has been increased so that every The number of records has been increased so that every attribute of every record has just one value.attribute of every record has just one value.

The multivalued attributes have been eliminated.The multivalued attributes have been eliminated.

Sales-personNumber

ProductNumber

Sales-personName


YearofHire

Depart-mentNumber

ManagerName

ProductName

UnitPrice

Quantity


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Sales-personNumber Product

Number

Sales-personName Commission

Percentage

YearofHire

Depart-mentNumber Manager

NameProductName

UnitPrice Quantity

137 19440 Baker 10 1995 73 Scott Hammer 17.50 473137 24013 Baker 10 1995 73 Scott Saw 26.25 170137 26722 Baker 10 1995 73 Scott Pliers 11.50 688186 16386 Adams 15 2001 59 Lopez Wrench 12.95 1745186 19440 Adams 15 2001 59 Lopez Hammer 17.50 2529186 21765 Adams 15 2001 59 Lopez Drill 32.99 1962186 24013 Adams 15 2001 59 Lopez Saw 26.25 3071204 21765 Dickens 10 1998 73 Scott Drill 32.99 809204 26722 Dickens 10 1998 73 Scott Pliers 11.50 734361 16386 Carlyle 20 2001 73 Scott Wrench 12.95 3729361 21765 Carlyle 20 2001 73 Scott Drill 32.99 3110361 26722 Carlyle 20 2001 73 Scott Pliers 11.50 2738


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First normal form is merely a starting point in the First normal form is merely a starting point in the normalization process.normalization process.

First normal form contains a great deal of data First normal form contains a great deal of data redundancy.redundancy. Three records involve salesperson 137, so there are Three records involve salesperson 137, so there are

three places in which his name is listed as Baker, his three places in which his name is listed as Baker, his commission percentage is listed as 10, and so on.commission percentage is listed as 10, and so on.

Two records involve product 19440 and this product’s Two records involve product 19440 and this product’s name is listed twice as Hammer and its unit price is name is listed twice as Hammer and its unit price is listed twice as 17.50. listed twice as 17.50.

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General Hardware Company: General Hardware Company: Second Normal FormSecond Normal Form

No Partial Functional DependenciesNo Partial Functional Dependencies Every nonkey attribute must be fully Every nonkey attribute must be fully

functionally dependent on the entire key of functionally dependent on the entire key of that table.that table.

A nonkey attribute cannot depend on only part A nonkey attribute cannot depend on only part of the key.of the key.

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In SALESPERSON, Salesperson Number is the sole In SALESPERSON, Salesperson Number is the sole primary key attribute. Every nonkey attribute of the table primary key attribute. Every nonkey attribute of the table is fully defined just by Salesperson Number.is fully defined just by Salesperson Number.

Similar logic for PRODUCT and QUANTITY tables.Similar logic for PRODUCT and QUANTITY tables.

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SalespersonNumber

SalespersonName


YearofHire

DepartmentNumber

ManagerName

137 Baker 10 1995 73 Scott186 Adams 15 2001 59 Lopez204 Dickens 10 1998 73 Scott361 Carlyle 20 2001 73 Scott

SALESPERSON Table

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General Hardware Company: General Hardware Company: Third Normal FormThird Normal Form

Does not allow transitive dependencies in Does not allow transitive dependencies in which one nonkey attribute is functionally which one nonkey attribute is functionally dependent on another.dependent on another.

Nonkey attributes are not allowed to define Nonkey attributes are not allowed to define other nonkey attributes.other nonkey attributes.

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Important points about the third normal form Important points about the third normal form structure are:structure are:

It is completely free of data redundancy.It is completely free of data redundancy.

All foreign keys appear where needed to logically tie All foreign keys appear where needed to logically tie together related tables.together related tables.

It is the same structure that would have been derived It is the same structure that would have been derived from a properly drawn entity-relationship diagram of from a properly drawn entity-relationship diagram of the same business environment.the same business environment.

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Candidate Keys as Candidate Keys as DeterminantsDeterminants

There is one exception to the rule that in third There is one exception to the rule that in third normal form, nonkey attributes are not allowed normal form, nonkey attributes are not allowed to define other nonkey attributes.to define other nonkey attributes.

The rule does not hold if the defining nonkey The rule does not hold if the defining nonkey attribute is a candidate key of the table.attribute is a candidate key of the table.

Candidate keys in a relation may define other Candidate keys in a relation may define other nonkey attributes without violating third normal nonkey attributes without violating third normal form.form.

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General Hardware Company: General Hardware Company: Functional DependenciesFunctional DependenciesSalesperson Number Salesperson NameSalesperson Number Commission PercentageSalesperson Number Year of HireSalesperson Number Department NumberSalesperson Number Manager NameCustomer Number Customer NameCustomer Number Salesperson NumberCustomer Number HQ CityCustomer Number, Employee Number Employee NameCustomer Number, Employee Number TitleProduct Number Product NameProduct Number Unit PriceDepartment Number Manager NameSalesperson Number, Product Number QuantityOffice Number TelephoneOffice Number Salesperson NumberOffice Number Size

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YearofHire

DepartmentNumber

ManagerName

CustomerName HQ

City

EmployeeName Title

ProductName

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Good Reading Bookstores: Good Reading Bookstores: Functional DependenciesFunctional Dependencies

Publisher Name CityPublisher Name CountryPublisher Name TelephonePublisher Name Year FoundedAuthor Number Author NameAuthor Number Year BornAuthor Number Year DiedBook Number Book NameBook Number Publication YearBook Number PagesBook Number Publisher NameCustomer Number Customer NameCustomer Number StreetCustomer Number CityCustomer Number StateCustomer Number Country

Book Number, Author Number null (or)Book Number Author NumberAuthor Number Book Number

Book Number, Customer Number, Date, Price QuantityBook Number, Customer Number, Date Quantity

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World Music Association: World Music Association: Functional DependenciesFunctional Dependencies

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Lucky Rent-A-Car:Lucky Rent-A-Car:Functional DependenciesFunctional Dependencies

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Data Normalization CheckData Normalization Check

The basic idea in checking the structural The basic idea in checking the structural worthiness of relational tables, created worthiness of relational tables, created through E-R diagram conversion, with the through E-R diagram conversion, with the data normalization rules is to:data normalization rules is to: Check to see if there are any partial functional Check to see if there are any partial functional

dependencies. dependencies.

Check to see if there are any transitive Check to see if there are any transitive dependencies.dependencies.

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Chapter 7 Logical Database Design Fundamentals of Database Management Systems by Mark L. Gillenson, Ph.D. University of Memphis Presentation by: Amita