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Maria's System Analysis Web Site

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Methodologies

Project Management

Data Flow Diagrams

Requirement Analysis

Questionnaire

DFDs

Symbols

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Squares representing external entities, which are sources or destinations of data.

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Rounded rectangles representing processes, which take data as input, do something to it, and output it.

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Arrows representing the data flows, which can either be electronic data or physical items.

bulletOpen-ended rectangles representing data stores, including electronic stores such as databases or XML files and physical stores such as or filing cabinets or stacks of paper.

Rules

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All processes must have at least one data flow in and one data flow out.

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All processes should modify the incoming data, producing new forms of outgoing data.

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Each data store must be involved with at least one data flow.

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Each external entity must be involved with at least one data flow.

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A data flow must be attached to at least one process.

 

Dataflow Diagram Level 0 - Context Diagram

 

Shows an overall summary the data inputs and outputs of the system.

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Dataflow Diagram Level 1

Specifies the inputs and outputs seen on the context diagram, and shows how this data flows through the system.

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Dataflow Diagram Level 2

There can be one level 2 DFD for each process of the Level 1 DFD.  Level 2 shows a process broken down into greater detail.  Level 2 Diagrams are only necessary where the Level 1 process is more complex, and where the particular process is relevant to the analysis.

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