© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 1 Chapter 8 Structuring System Logical Requirements

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 2 Learning Objectives 10.Describe the modeling of process decision logic.  Use Structured English as a tool for representing steps in logical processes in DFDs.  Use decision tables and decision trees to represent the logic of choice in conditional statements.  Select among Structured English, decision tables, and decision trees for representing processing logic.  Understand how logic modeling techniques apply to the development of Internet applications.

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 3

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 4 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.

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 5 Logic Modeling Deliverables and Outcomes: Structured English Decision Tables Decision Trees State-transition diagrams Sequence diagrams Activity diagrams

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 6 Modeling Logic with Structured English Uses modified form of English to specify the logic of information processes Uses a subset of English  Action verbs  Noun phrases  No adjectives or adverbs Has no specific standards

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 7

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 8 Structured English is used here to describe input and output.

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 9 Structured English is used here to describe arithmetic operations.

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 10 Structured English is used here to describe repetition.

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 11 Structured English is used here to describe decisions.

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 12 Structured English is used here to describe invoking other processes.

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 13 Modeling Logic with Decision Tables A matrix representation of the logic of a decision. Used to specify the possible conditions and the resulting actions. Best used for complicated decision logic.

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 14 3 Parts of a Decision Table 1.Condition stubs  List 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  Condition whose value does not affect which action is taken for two or more rules.

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 15 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.

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 16 Decision Table Note: for salaried employees the action stub chosen will always be the same…therefore hours worked is an indifferent condition

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 17 Reduced Decision Table Because of indifferent condition, the complete decision table can be reduced to one with fewer rules.

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 18 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  Decision points represented by nodes.  Actions represented by ovals.  Particular choices from a decision point represented by arcs.

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 19 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.

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 20 Decision tree representation of salary decision

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 21 Alternative decision tree representation of salary decision

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 22 Deciding Among Structured English, Decision Tables, and Decision Trees CriteriaStructured English Decision Tables Decision Trees Determining Conditions and Actions Second BestThird BestBest Transforming Conditions and Actions into Sequence BestThird BestBest Checking Consistency and Completeness Third BestBest

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 23 Deciding Between Decision Tables and Decision Trees CriteriaDecision TablesDecision Trees Portraying complex logic BestWorst Portraying simple rules WorstBest Making decisionsWorstBest More compactBestWorst Easier to manipulateBestWorst

© 2006 ITT Educational Services Inc. SE350 System Analysis for Software Engineers: Unit 8 Slide 24 Summary In this chapter you learned how to: 10.Describe the modeling of process decision logic.  Use Structured English as a tool for representing steps in logical processes in DFDs.  Use decision tables and decision trees to represent the logic of choice in conditional statements.  Select among Structured English, decision tables, and decision trees for representing processing logic.  Understand how logic modeling techniques apply to the development of Internet applications.