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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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1. Data Flow Diagramsfor 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