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Logic Requirements
Modern Systems Analysisand Design
© 2008 by Prentice Hall 2Chapter 8
Learning Objectives
Use Structured English as a tool for representing steps in logical processes in data flow diagrams.
Use decision tables to represent the logic of choice in conditional statements.
© 2008 by Prentice Hall 3Chapter 8
Learning Objectives (Cont.)
Select among Structured English and decision tables for representing processing logic.
Understand how logic modeling techniques apply to the development of electronic commerce applications.
© 2008 by Prentice Hall 4Chapter 8
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.
Modeling a System’s Logic
© 2008 by Prentice Hall 5Chapter 8
© 2008 by Prentice Hall 6Chapter 8
Deliverables and Outcomes
Structured English representation of process logic.
Decision Tables representation. Sequence diagram. Activity diagram.
© 2008 by Prentice Hall 7Chapter 8
Modeling Logic with Structured English Structured English: modified form of
English language used to specify the logic of information system processes.
No single standard. Typically relies on action verbs and noun
phrases and contains no adjectives or No specific standards.
Modeling Logic with Structured English (Cont.)
© 2008 by Prentice Hall 8Chapter 8
Modeling Logic with Structured English (Cont.)
© 2008 by Prentice Hall 9Chapter 8
© 2008 by Prentice Hall 10Chapter 8
Modeling Logic with Decision Tables Decision table: a matrix representation of
the logic of a decision which specifies the possible conditions for the decision and the resulting actions.
Best used for complicated decision logic.
© 2008 by Prentice Hall 11Chapter 8
Modeling Logic with Decision Tables (Cont.)
© 2008 by Prentice Hall 12Chapter 8
Modeling Logic with Decision Tables (Cont.) Condition stubs: that part of a decision
table that lists the conditions relevant to the decision.
Action stubs: that part of a decision table that lists the actions that result for a given set of conditions.
© 2008 by Prentice Hall 13Chapter 8
Modeling Logic with Decision Tables (Cont.) Rules: that part of a decision table that
specifies which actions are to be followed for a given set of condition.
Indifferent condition: in a decision table, a condition whose value does not affect which actions are taken for two or more rules.
© 2008 by Prentice Hall 14Chapter 8
Modeling Logic with Decision Tables (Cont.) Procedure for Creating Decision Tables
Name the condition and the values that each condition can assume.
Name all possible actions that can occur.List all possible rules.Define the actions for each rule.Simplify the table.
© 2008 by Prentice Hall 15Chapter 8
Modeling Logic with Decision Tables (Cont.)
© 2008 by Prentice Hall 16Chapter 8
Deciding Among Structured English and Decision Tables
Criteria Structured English
Decision Tables
Determining Conditions and Actions
Second Best Third Best
Transforming Conditions and Actions into Sequence
Best Third Best
Checking Consistency and Completeness
Third Best Best
Electronic Commerce Application: Logic Modeling Pine Valley Furniture development
methodology dictated that the logic within each unique processes be represented.
Structured English was chosen for modeling the logic.
© 2008 by Prentice Hall 17Chapter 8
Electronic Commerce Application: Logic Modeling (Cont.)
© 2008 by Prentice Hall 18Chapter 8
Figure 8-8 Level-0 DFD for the WebStore system
Electronic Commerce Application: Logic Modeling (Cont.)
© 2008 by Prentice Hall 19Chapter 8
© 2008 by Prentice Hall 20Chapter 8
Summary In this chapter you learned how to:
Use Structured English as a tool for representing steps in logical processes in data flow diagrams.
Use decision tables to represent the logic of choice in conditional statements.
Select among Structured English and decision tables for representing processing logic.
Understand how logic modeling techniques apply to the development of electronic commerce applications.