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IT 21103/41103

IT 21103/41103. System Analysis & Design. Chapter 03. Process Modeling. Process Modeling. The analyst must fully understand the current system. Process Modeling. We use the Data Flow Diagram (DFD) to help us understand the current system. Process Modeling.

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IT 21103/41103

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  1. IT 21103/41103 System Analysis & Design

  2. Chapter 03 Process Modeling

  3. Process Modeling The analyst must fully understand the current system

  4. Process Modeling We use the Data Flow Diagram (DFD) to help us understand the current system

  5. Process Modeling DFDs model the people, procedures, and data components of the system

  6. Process Modeling DFDs are Process Models Process models direct our focus to the processes that transform data into information

  7. Process Modeling Data: A single (raw) fact about something Information: Organized data

  8. Process Modeling DFDs do not show enough detail about the system so we will develop Entity Relationship Diagrams later to provide this detail

  9. Data Flow Diagram A orderly picture of what the current system is supposed to do How data is transformed into information

  10. DFD Symbols External Entity Originator (source) or Receiver (sink) of Information

  11. DFD Symbols Process Series of steps that manipulates data

  12. DFD Symbols Data Store A place to keep data for later reference or use

  13. DFD Symbols Data Flow Line Data and/or Information transportation

  14. DFD Symbols Gane-Sarson DFD Symbol Set

  15. DFD Rules Data Flow Lines should never cross (may have to use an entity in more than one place – use a shaded lower corner to designate this entity is used elsewhere in the diagram)

  16. DFD Rules Data flows should not connect an external entity to a data store or to another external entity – there must be a process in between

  17. DFD Rules Data flows should not connect a data store directly to another data store - there must be a process in between

  18. DFD Rules Data Stores should have at least one entry data flow and one exit data flow and connects only to a process (an archive or backup data store has only one entry data flow)

  19. DFD Rules Each process must have a least one entry and exit data flow

  20. External Entities Bottom-up Approach Develop a narrative of the system Underline the action verbs Develop a sequential task list of action words Eliminate tasks that do not transform data

  21. External Entities Bottom-up Approach Cont’d Identify cohesive tasks Fit all remaining tasks to a cohesive task Develop an IPO chart for each cohesive task

  22. Input-Process-Output (IPO) IPO Chart is a framework for producing the DFD Input Data Processing Output Information

  23. Context Diagram Precedes the DFD It is a more abstract model showing the entire system at a glance The broad picture of the system

  24. Rio System Context Diagram External entities are described and data flows in and out of the system are represented in the diagram Student Teacher Login/Logout Email Email Login/Logout

  25. Rio System Context Diagram Why are students and teachers not considered Internal Entities? We have no control over them, therefore they are external entities Student Teacher Login/Logout Email Email Login/Logout

  26. Decomposition We need to get details about the system so we decompose the Context Diagram to form the DFD

  27. Decomposition We begin by identifying the individual events within the system We must distinguish between Events ( a benchmark or measurement) and Tasks (the process)

  28. First Level DFD Created when all the IPOs are finished, the 1st level DFD shows the separate processes that compose the system

  29. Data Flows Show connection between entities and processes, but also show the data or information that flows within the diagram

  30. Data Flows Make the descriptions as detailed as necessary to convey your meaning.

  31. When to stop decomposition When you no longer gain any new insight on how the system works.

  32. Important considerations! The Context Diagram and DFD are only models. They should represent reality as much as possible, but they only provide a logical representation of the system

  33. Important considerations! DFDs do not represent the complete system, so be careful to use it as a guide, not as the final tool to understanding the current system.

  34. Important considerations! End users are rarely concerned with looking at or understanding DFDs. Do Not Spend lots of time making them look pretty, but you should not skip creating them.

  35. Questions?

  36. Assignment 03 Page 93 - 1-6 Due: Sept 28th, 2005

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