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Chapter 8 Structuring System Logical Requirements

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  1. Modern Systems Analysisand DesignFourth EditionJeffrey A. Hoffer Joey F. GeorgeJoseph S. Valacich Chapter 8 Structuring System Logical Requirements

  2. 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.

  3. 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.

  4. Logic Modeling Deliverables and Outcomes • Structured English • Decision Tables • Decision Trees • State-transition diagrams • Sequence diagrams • Activity diagrams

  5. 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

  6. Structured English is used here to describe input and output.

  7. Structured English is used here to describe arithmetic operations.

  8. Structured English is used here to describe repetition.

  9. Structured English is used here to describe decisions.

  10. Structured English is used here to describe invoking other processes.

  11. 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

  12. 3 Parts of a Decision Table • Condition stubs • Lists condition relevant to decision • Action stubs • Actions that result from a given set of conditions • 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

  13. 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

  14. Decision Table Note: for salaried employees the action stub chosen will always be the same…therefore hours worked is an indifferent condition

  15. Reduced Decision Table Because of indifferent condition, the complete decision table can be reduced to one with fewer rules

  16. 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

  17. 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

  18. Decision tree representation of salary decision

  19. Alternative decision tree representation of salary decision

  20. Deciding Among Structured English, Decision Tables, and Decision Trees

  21. Deciding Between Decision Tables and Decision Trees

  22. 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 and decision trees to represent logical choice in conditional statements. • Select among structured English, decision tables, and decision trees.