chapter3-relational database2

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Chapter 3The Relational Database Model

(Part 2)


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OBJECTIVE:

After learn this chapter, students will

Explain the logical view of the data in relational database model

Define the relational models basic components.

Explain how entities and their attributes are organized into

tables.

Analyses the difference between data dictionary and system

catalog

Explain how data redundancy is handled in the relational

database model.


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A Logical View of Data Relational database models structural and

data independence enables us to view data

logically rather than physically.

The logical view allows a simpler fileconcept of data storage.

The use of logically independent tables is

easier to understand.

Logical simplicity yields simpler and more

effective database design methodologies.


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A Logical View of Data Entities and Attributes

An entity is a person, place, event, or thingfor which we intend to collect data.

University -- Students, Faculty Members, Courses

Airlines -- Pilots, Aircraft, Routes, Suppliers

Each entity has certain characteristicsknown as attributes.

Student -- Student Number, Name, GPA, Date ofEnrollment, Data of Birth, Home Address, Phone

Number, Major

Aircraft -- Aircraft Number, Date of Last

Maintenance, Total Hours Flown, Hours Flownsince Last Maintenance


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A Logical View of Data

Entities and Attributes

A grouping of related entities becomes an

entity set.

The STUDENT entity set contains all studententities.

The FACULTY entity set contains all facultyentities.

The AIRCRAFT entity set contains all aircraftentities.


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A Logical View of Data

Tables and Their Characteristics

A table contains a group of relatedentities -- i.e. an entity set.

The terms entity set and table are often

used interchangeably.

A table is also called a relation.


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Keys Controlled redundancy (shared common

attributes) makes the relational databasework.

Theprimary key of one table appears againas the link (foreign key) in another table.

If the foreign key contains either matchingvalues or nulls, the table(s) that make use ofsuch a foreign key are said to exhibit

referential integrity.


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Keys

Akey helps define entity relationships.

The keys role is based on a concept known asdetermination, which is used in the definition offunctional dependence.

The attribute B is functionally dependent on A if Adetermines B.

An attribute that is part of a key is known as a keyattribute.

A multi-attribute key is known as a composite key.

If the attribute (B) is functionally dependent on acomposite key (A) but not on any subset of thatcomposite key, the attribute (B) is fully functionallydependent on (A).


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Relational Database Keys

Table 2.3


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Integrity Rules Revisited

Table 2.4


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The Data Dictionary and

the System Catalog Data dictionary contains metadata to provide detailed accounting of

all tables within the database.

System catalog is a very detailed system data dictionary that describes

all objects within the database.

System catalog is a system-created database whose tables store

the database characteristics and contents.

System catalog tables can be queried just like any other tables.

System catalog automatically produces databasedocumentation.


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A Sample Data Dictionary

Table 2.6


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Relationships within the Relational

Database

E-R Diagram (ERD)

Rectangles are used to represent entities.

Entity names are nouns and capitalized.

Diamonds are used to represent therelationship(s) between the entities.

The number 1 is used to represent the 1side of the relationship.

The letter M is used to represent the many

sides of the relationship.


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The Relationship Between Painter and Painting

Figure 2.17


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An Alternate Way to Present the Relationship

Between Painter and Painting

Figure 2.18


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A 1:M Relationship: The CH2_MUSEUM Database

Figure 2.19


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The 1:M Relationship Between Course and Class

Figure 2.20


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The M:N Relationship Between Student and Class

Figure 2.22


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Table 2.7

Sample Student Enrollment Data


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A Many-to-Many Relationship Between Student and Class

Figure 2.23


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Changing the M:N Relationship to Two 1:M Relationships

Figure 2.25


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The Expanded Entity Relationship Model

Figure 2.26


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The Relational Schema for the Entity Relationship Diagram

in Figure 2.26

Figure 2.27


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Data Redundancy Revisited

Proper use of foreign keys is crucial toexercising data redundancy control.

Database designers must reconcile threeoften contradictory requirements: designelegance, processing speed, and informationrequirements. (Chapter 4)

Proper data warehousing design evenrequires carefully defined and controlleddata redundancies, to function properly.

(Chapter 13)


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The redundancy is crucial to the systems success.

Copying the product price from the PRODUCT table

to the LINE table means that it is possible to

maintain the historical accuracy of the transactions.

Figure 2.29

The Relational Schema for the Invoicing System in Figure 2.28

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