Lesson 6 - Data Flow Diagrams
What is a data flow diagram?
This is a diagrammatical way of explaining how information flows around a system. You normally start by drawing a general overview of a system (high-level DFD) and then progress to more detailed and complex diagrams (low-level DFDs). A high-level DFD is also called a CONTEXT DIAGRAM.
There are certain rules you must follow when drawing a DFD.
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External Entities The ellipse is used to identify external entities such people, departments, other systems and organisations etc which exchange data with the system being analysed. The ellipse contains a unique identifier name for this type of entity.
Note that this represents a type of entity not a single occurrence of that
entity. i.e. the entity can represent all suppliers |
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Processes
This symbol is used to represent a process. The top left carries a
unique identifier, top right identifies the location of the process (e.g.
Sales Office). The body of the box contains the name of the process (e.g.
Create customer order). |
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Data Stores Data stores are represented by a double box. The left hand box contains a unique identifier. A prefix for the unique identifier is used to identify the store type: D for digital data (ie database) , M for Manual data (ie filing cabinet), T for Transient (ie temp location such as an in-tray or e-mail). The right hand side should describe its contents not its location
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Data Flows
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