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Chapter 6

Chapter 6. The Traditional Approach to Requirements. Objectives. Explain how the traditional approach and the object-oriented approach differ when an event occurs List the components of a traditional system and the symbols representing them on a data flow diagram

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Chapter 6

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  1. Chapter 6 The Traditional Approach to Requirements Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  2. Objectives • Explain how the traditional approach and the object-oriented approach differ when an event occurs • List the components of a traditional system and the symbols representing them on a data flow diagram • Describe how data flow diagrams can show the system at various levels of abstraction Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  3. Objectives • Develop data flow diagrams, data element definitions, data store definitions, and process descriptions • Develop tables to show the distribution of processing and data access across system locations • Read and interpret information engineering models that can be incorporated within traditional structured analysis Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  4. Traditional versus OO ApproachesFigure 6-1 Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  5. Data Flow Diagrams • Graphical system model that shows all main requirements for an IS • Inputs / outputs • Processes • Data storage • Easy to read and understand Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  6. Data Flow Diagram SymbolsFigure 6-2 Process Step-by-step instructions Data flow External agent Data store Data at rest Real-time link Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  7. DFD Fragment from the RMO Case Figure 6-3 Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  8. DFD Integrates Event Table and ERDFigure 6-4 Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  9. DFD and Levels of Abstraction • DFDs are decomposed into additional diagrams to provide multiple levels of detail • Higher levels are more general • Lower levels are more detailed Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  10. Layers of DFD Abstraction Figure 6-5 Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  11. Context Diagrams • DFD that summarizes all processing activity • Highest level view of system • Shows system boundaries • Scope is represented by a single process and outside agents Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  12. DFD Fragments • Represents system response to one event within a single process symbol • Self contained model • Focuses attention on single part of system • Shows only data stores required to respond to events Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  13. Context Diagram for RMO Order-Entry Subsystem Figure 6-8 Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  14. Two DFD Fragments for RMO Order-Entry System Figure 6-10 Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  15. Event Partitioned System Model • DFD that models system requirements using a single process for each event in a system or subsystem • Sometimes called diagram 0 • Decomposition of the context level diagram • Is decomposed into more detailed DFD fragments Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  16. Combining DFD Fragments Figure 6-11 Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  17. Decomposing DFD Fragments • Sometimes DFD fragments need to be explored in more detail • Broken into subprocesses with additional detail • Numbering scheme doesn’t equate to execution sequence Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  18. Detailed Diagram for Create New Order Figure 6-13 Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  19. Physical and Logical DFDs • Logical model • Assumes implementation in perfect technology • Does not tell how system is implemented • Physical model • Describes assumptions about implementation technology • Developed in last stages of analysis or in early design Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  20. Evaluating DFD Quality • Readable • Internally consistent • Accurately represents system • Reduces information overload • Rule: 7 +/- 2 • Minimizes required number of interfaces Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  21. Data Flow Consistency Problems • Differences in data flow content between a process and its process decomposition • Data outflows without corresponding inflows • Data inflows without corresponding outflows • Results in unbalanced DFDs Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  22. Consistency Rules • All data that flows into a process must flow out or be used to generate data that flows out • All data that flows out of a process must have flowed in or been generated from data that flowed in Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  23. Unnecessary Data Input: Black Hole Figure 6-15 Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  24. Process with Impossible Data Output: Miracle Figure 6-16 Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  25. Process with Unnecessary Data Input Figure 6-17 Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  26. Process with Impossible Data Output Figure 6-18 Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  27. Documentation of DFD Components • Lowest level processes need to be described in detail • Data flow contents need to be described • Data stores need to be described in terms of data elements • Each data element needs to be described • Various options for process definition exist Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  28. Structured English • Method of writing process specifications that combines structured programming techniques with narrative English • Well suited to lengthy sequential processes or simple control logic • Ill-suited for complex decision logic or few sequential processing steps Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  29. Process 2.1 and Structured English Process Description Figure 6-20 Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  30. Decision Tables and Decision Trees • Can summarize complex decision logic better than structured English • Incorporates logic into the table or tree structure to make descriptions more readable Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  31. Data Flow Definitions • Textual description of data flow’s content and internal structure • Often coincide with attributes of data entities included in ERD Data Flow Definitions Simply Listing ElementsFigure 6-25 Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  32. Data Element Definitions • Data type description • e.g. string, integer, floating point, Boolean • Very specific • Length of element • Maximum and minimum values Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  33. Components of a Traditional Analysis Mode Figure 6-30 Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  34. Information Engineering Models • Focuses on strategic planning and data requirements of new system • Shares features with structured system development methodology • Developed by James Martin in early 1980’s Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  35. Information Engineering System Development Life Cycle Phases Figure 6-31 Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  36. Process Decomposition and Dependency Models • IE process model information types • Decomposition of processes into other processes • Dependency relationships among processes • Internal processing logic Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  37. Process Dependency Diagram Figure 6-34 Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  38. Process Dependency Diagram with Data Flows Figure 6-35 Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  39. Locations and Communication Through Networks • Logical information needed during analysis • Number of user locations • Processing and data access requirements at various locations • Volume and timing of processing and data access requests • First, identify locations where work is to be performed Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  40. RMO Location Diagram Figure 6-36 Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  41. Location Considered • List functions performed by users at each location • Place in matrix • Rows are system activities • Columns are locations • Other matrices • Activities versus data Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

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