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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. Course Registration System Context Diagram Academic Department Schedule Data Enrollment Request Faculty Member Student Class List Schedule Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  12. Student List Student List Schedule Course Enroll Student Produce Class List Course enrollment Course enrollment Offered Course Offered Course Offered Course DFD Fragments Schedule data Academic Department Enrollment Request Student Schedule Class List Faculty Member Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  13. Student List Course enrollment Produce Class List Enroll Student Schedule Course Offered Course Diagram 0 Enrollment Request 2 Student Academic Department Schedule Schedule data 1 3 Class List Faculty Member Systems Analysis and Design in a Changing World, 2nd Edition, Satzinger, Jackson, & Burd

  14. 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

  15. 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

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

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

  18. 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

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

  20. 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

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

  22. 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

  23. 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

  24. 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

  25. 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

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

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

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

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

  30. 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

  31. 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

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

  33. 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

  34. 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

  35. 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

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

  37. 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

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

  39. 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

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

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

  42. 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

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

  44. 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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