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Chapter 6
Database Design 2:
Design Methodology
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Objectives

Discuss the general process and goals of
database design

Define user views and explain their
function

Define database design language and use
it to document database designs

Create an entity-relationship diagram to
visually represent a database design
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 Present
a methodology for database
design at the information level and view
examples illustrating this methodology
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Objectives

Explain the physical-level design process

Examine some alternative approaches to
entity-relationship diagrams

Discuss top-down and bottom-up
approaches to database design and
examine the advantages and
disadvantages of both methods

Use a survey form to obtain information
from users prior to beginning the
database design process
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Objectives
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 Review
existing documents to obtain
information from users prior to beginning
the database design process
 Discuss
special issues related to
implementing one-to-one relationships
and many-to-many relationships involving
more than two entities
 Discuss
entity subtypes and their
relationships to nulls
 Learn
how to avoid potential problems
when merging third normal form relations
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Database Design
 User

Views
Requirements necessary to support a particular
user’s operations
 Information-level




Design Methodology
Represent user view as collection of tables
Normalize these tables
Identify all keys
Merge the result into design
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Represent User View as
Collection of Tables
Step 1:
Step 2:
Step 3:
Step 4:
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Determine entities involved and
create separate table for each
type
Determine primary key for each
table
Determine properties for each
entities
Determine relationships among
entities
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Normalize the Tables
 Represent

Primary, alternate, secondary, foreign
 Database

all keys
Design Language (DBDL)
Mechanism for representing tables and keys
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DBDL Notation
 Table
name followed by columns in
parentheses

Primary key column(s) underlined
 AK
identifies alternate keys
 SK identifies secondary keys
 FK identifies foreign keys
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Entity-Relationship Diagrams
Figure 6.2
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Merge the Result into the Design
Figure 6.3
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User View Examples
View #1: Sales Rep View
Rep (RepNum, LastName, FirstName, Street,
City, State, Zip, Commission, Rate)
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User View Examples (con’t.)
Figure 6.5
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View #2: Customer View
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User View Examples (con’t.)
Figure 6.6
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View #3: Part View
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User View Examples (con’t.)
Figure 6.8
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View #4: Order View
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Second Set User View Examples
View #1: Publisher View
Publisher (PublisherCode, PublisherName, City)
SK PublisherName
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Second Set User View Examples
(con’t.)
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View #2: Branch View
Publisher (PublisherCode, PublisherName, City)
SK PublisherName
Branch (BranchNum, BranchName,
BranchLocation, NumEmployees)
SK BranchName
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Second Set User
View Examples (con’t.)
Figure 6.11
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View #3: Book View
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Second Set User
View Examples (con’t.)
Figure 6.12
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View #4: Author View
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Second Set User
View Examples (con’t.)
Figure 6.13
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View #5 and View #6: Inventory View
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Physical-Level Design
 Undertaken
after information-level design
completion
 Most DBMSs support primary, candidate,
secondary, and foreign keys
 DB programmers must include logic to
ensure the uniqueness of primary keys and
enforce other conditions
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ERD Relationship Alternative
Figure 6.14
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Symbols for Columns
Figure 6.15
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Composite Entity
Figure 6.16
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Crow’s Foot Symbol
Figure 6.17
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Representing Cardinality
Figure 6.18
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Top-Down vs. Bottom-Up
 Bottom-up


Design starts at low level
Specific user requirements drive design process
 Top-down


Begins with general database that models overall
enterprise
Refines the model until design is achieved
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Survey Form
 Used
to collect information from users
 Must contain particular elements





Entity information
Attribute information
Relationships
Functional dependencies
Processing information
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Existing Documents
 Aid
in collecting user requirements
 Collect information similar to that collected
with survey forms





Entity information
Attribute information
Relationships
Functional dependencies
Processing information
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1:1 Relationship Considerations
Figure 6.25
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Include primary key of
each table as foreign
key in the other
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1:1 Relationship Considerations
Figure 6.26
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Implementation when
information does not
match.
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1:1 Relationship Considerations
Figure 6.27
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Implemented in a single
table.
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1:1 Relationship Considerations
Figure 6.28
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1:1 relationship implemented by
including primary key of one table
as foreign key (and alternative key)
in the other.
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M:M Relationship Considerations
Figure 6.29
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Sample Sales Data
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M:M Relationship Considerations
Figure 6.30
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Result obtained by splitting
Sales table into three tables
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M:M Relationship Considerations
Figure 6.31
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Result obtained by joining three tables--2 rows
are in error. Must be converted to 4NF.
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Table Split to Avoid Nulls
Figure 6.32
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Nulls are absence
of values
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Entity Subtypes
Figure 6.34
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Student Table Split to
Avoid Nulls
Figure 6.36
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Two Entity Subtypes—
Incomplete Categories
Figure 6.37
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Two Entity Subtypes—
Complete Categories
Figure 6.38
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