Modern Systems Analysis
and Design
Fourth Edition
Jeffrey A. Hoffer
Joey F. George
Joseph S. Valacich
Chapter 8
Structuring System Logical
Requirements
© 2005 by Prentice Hall
Learning Objectives
Use structured English as a tool for
representing steps in logical processes in
data flow diagrams.
Use decision tables and decision trees to
represent logical choice in conditional
statements.
Select among structured English, decision
tables, and decision trees.
8-2
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8-3
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Logic Modeling
Data flow diagrams do not show the
logic inside the processes.
Logic modeling involves representing
internal structure and functionality of
processes depicted on a DFD.
Logic modeling can also be used to
show when processes on a DFD occur.
8-4
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Logic Modeling Deliverables and
Outcomes
Structured English
Decision Tables
Decision Trees
State-transition diagrams
Sequence diagrams
Activity diagrams
8-5
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Modeling Logic with
Structured English
Modified form of English used to specify
the logic of information processes
Uses a subset of English



Action verbs
Noun phrases
No adjectives or adverbs
No specific standards
8-6
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8-7
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Structured English is
used here to describe
input and output.
8-8
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Structured English is
used here to describe
arithmetic operations.
8-9
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Structured English is
used here to
describe repetition.
8-10
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Structured English is
used here to
describe decisions.
8-11
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Structured English is used
here to describe invoking
other processes.
8-12
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Modeling Logic with
Decision Tables
A matrix representation of the logic of a
decision
Specifies the possible conditions and
the resulting actions
Best used for complicated decision logic
8-13
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3 Parts of a Decision Table
1. Condition stubs

Lists condition relevant to decision
2. Action stubs

Actions that result from a given set of conditions
3. Rules

Specify which actions are to be followed for a given set of
conditions
Indifferent Condition

8-14
Condition whose value does not affect which action is
taken for two or more rules
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Procedure for Creating
Decision Tables
Name the condition and values each
condition can assume
Name all possible actions that can occur
List all rules
Define the actions for each rule
Simplify the table
8-15
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Decision Table
Note: for salaried employees the action stub chosen will always
be the same…therefore hours worked is an indifferent condition
8-16
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Reduced Decision Table
Because of indifferent condition, the complete decision table
can be reduced to one with fewer rules
8-17
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Modeling Logic with Decision
Trees
A graphical representation of a decision
situation
Decision situation points are connected
together by arcs and terminate in ovals
Main components



8-18
Decision points represented by nodes
Actions represented by ovals
Particular choices from a decision point
represented by arcs
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Modeling Logic with Decision
Trees (cont.)
Read from left to right
Each node corresponds to a numbered
choice on a legend
All possible actions are listed on the far
right
8-19
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Decision tree representation of salary
decision
8-20
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Alternative decision tree representation of
salary decision
8-21
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Deciding Among Structured English,
Decision Tables, and Decision Trees
Criteria
Structured Decision
English
Tables
Decision
Trees
Determining
Second Best
Conditions and
Actions
Third Best
Best
Transforming
Best
Conditions and
Actions into
Sequence
Third Best
Best
Checking
Consistency
and
Completeness
Best
Best
8-22
Third Best
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Deciding Between Decision Tables
and Decision Trees
Criteria
Decision Tables Decision Trees
Portraying
Best
complex logic
Portraying simple Worst
rules
Worst
Making decisions Worst
Best
More compact
Best
Worst
Easier to
manipulate
Best
Worst
8-23
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Best
Summary
In this chapter you learned how to:



8-24
Use structured English as a tool for
representing steps in logical processes in
data flow diagrams.
Use decision tables and decision trees to
represent logical choice in conditional
statements.
Select among structured English, decision
tables, and decision trees.
© 2005 by Prentice Hall