... have input and output (if it is not dead), so a process must have input and output. * Data enters the system from the environment; data flows between processes within the system; and data is produced as output from the system. An example: The 'Context Diagram ' is an overall, simplified, view of the target system, which contains only one process box, and the primary inputs and outputs. Context diagram 1 Context diagram 2 Both the above diagrams say the same thing. The second makes use of the possibility in SSADM of including duplicate objects. (In context diagram 2 the duplication of the Customer object is shown by the line at the left hand side. Drawing the diagram in this way emphasizes the Input-Output properties of a system. The Context diagram above, and the decomposition which follows, are a first attempt at describing part of a 'Home Catalogue' sales system. In the ...

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