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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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