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Data Flow Diagrams for GIS

Data Flow Diagrams. A graphical means of presenting or describing a process (or series of processes) by drawing symbols which represent sequential steps in a chain of operationsA pictorial shorthand for recording and presenting work flowsInputs are connected to Outputs by ProcessesThese connections are shown by arrows which represent sequence and dependency (i.e., X must be done before Y can be done)Also known as a Process Flow Diagram or Flow Chart.

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Data Flow Diagrams for GIS

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    1. Data Flow Diagrams for GIS

    2. Data Flow Diagrams

    3. Symbols (typical – but not what we’ll use…) Input (Square) Process (Bubble) Data Flow (Line) Output (Rectangle) .

    4. Symbols - that we will be using (corresponding with ArcGIS ModelBuilder) INPUT (Blue Oval) PROCESS (Yellow Rectangle) DATA FLOW (Arrow) OUTPUT (Green Oval) Use Annotation to support Diagram as necessary

    5. Non-GIS Example…

    6. Non-GIS Example…

    7. Non-GIS Example…

    8. Non-GIS Example…

    9. Non-GIS Example…

    10. Non-GIS Example…

    11. GIS Example…

    12. INPUT Symbol Every Data Flow Diagram must have at least one INPUT (External Entity) Data cannot flow directly from one Input to another Data cannot flow directly from an Input to an Output You must have a Process between the Inputs and Outputs that transforms the data

    13. Thus, these diagrams would be incorrect. INPUT Symbol

    14. Thus, these diagrams would be incorrect. INPUT Symbol

    15. These diagrams would be correct. INPUT Symbol

    16. Every Data Flow Diagram must have at least one PROCESS or Operation Processes change the data. They will always be an action (contain a verb) A Process requires at least one Input and one Output Data is transformed as it flows through the Process PROCESS Symbol

    17. You cannot have data flowing in without data flowing out This is known as a Black Hole This diagram would be incorrect. The arrowheads show data flowing in but nothing flowing out PROCESS Symbol

    18. You cannot have data flowing in without data flowing out This is known as a Black Hole This diagram would be incorrect. The arrowheads show data flowing in but nothing flowing out PROCESS Symbol

    19. You cannot have data flowing out without data flowing in This is known as a Miracle This diagram would be incorrect. The arrowheads show the data flowing out but nothing flowing in PROCESS Symbol

    20. You cannot have data flowing out without data flowing in This is known as a Miracle This diagram would be incorrect. The arrowheads show the data flowing out but nothing flowing in PROCESS Symbol

    21. This diagram would be correct. PROCESS Symbol

    22. This diagram would be incorrect (undesirable).* PROCESS Symbol

    23. This diagram would be incorrect (undesirable).* PROCESS Symbol

    24. Thus, this diagram would be correct (preferred). PROCESS Symbol

    25. Every Data Flow Diagram must have at least one OUTPUT (Derived Entity) The only DFD without an output is the Delete tool… The purpose of a DFD is to describe the Process of creating an Output Data cannot flow directly from an Input to an Output You must have a process between the Input and the Output that transforms the data Derived (Output) Data can become the Input data for another Process (an intermediate Output)

    26. Data can be both an Output and an Input Some ‘Outputs’ are ‘Virtual Outputs’ Not necessarily a whole new data layer (e.g., a selection subset) Virtual Outputs are still shown on Data Flow Diagram

    27. Data Flows should show the direction of the data flow using arrowheads Data flows in only one direction (Especially w/GIS) A Data Flow should not cross another Data Flow This data flow would be undesirable

    28. Bends or curves are fine This data flow would be correct

    29. Can become quite complicated… Data can be both an output and an input Data can serve as an input for multiple processes This data flow would be correct

    30. Philosophy of Design/Development DFD’s use a “Top Down” Planning Philosophy Start with the global picture Identify possible inputs, desired outputs Work towards detail one level at a time Test possible processes and analysis sequences An iterative process of design – test – modify – test…

    31. Philosophy of Design/Development DFD’s use a “Top Down” Planning Philosophy Start with the global picture Identify possible inputs, desired outputs Work towards detail one level at a time Test possible processes and analysis sequences An iterative process of design – test – modify – test…

    32. Philosophy of Design/Development DFD’s use a “Top Down” Planning Philosophy Start with the global picture Identify possible inputs, desired outputs Work towards detail one level at a time Test possible processes and analysis sequences An iterative process of design – test – modify – test…

    33. Philosophy of Design/Development DFD’s use a “Top Down” Planning Philosophy Start with the global picture Identify possible inputs, desired outputs Work towards detail one level at a time Test possible processes and analysis sequences An iterative process of design – test – modify – test…

    34. ANNOTATION ANNOTATION (labels) can be used to record details (parameters) of the Processes as well as data locations This information could also be contained in a footnote

    35. ANNOTATION - Footnotes (in addition to or in lieu of annotation within the DFD)

    36. fini

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