Logic Requirements Modern Systems Analysis and Design.

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.


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.


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



Deliverables and Outcomes

Structured English representation of process logic.

Decision Tables representation. Sequence diagram. Activity diagram.


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.)



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.


Modeling Logic with Decision Tables (Cont.)


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.


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.


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.


Modeling Logic with Decision Tables (Cont.)


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.


Electronic Commerce Application: Logic Modeling (Cont.)


Figure 8-8 Level-0 DFD for the WebStore system

Electronic Commerce Application: Logic Modeling (Cont.)



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.

Logic Requirements Modern Systems Analysis and Design.

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