Like the Context Data Flow Diagram, the
Decomposition Diagram is another tool that illustrates the processes of
an information system. Because many information systems prove to be quite complex, the aim of this tool is to
break down (“decompose”) this complexity. As indicated below, typically the Decomposition Diagram will start
with a top-level symbol indicating “The System.” Underneath this symbol, the system is broken down into its
key functions. Below each function, the diagram indicates the essential activities of this part of the system.
Some of the activities are broken down into a series of tasks (note: usually all activities are broken down into
associated tasks, but in the interest of space, this diagram doesn’t go that far). Each symbol is numbered to
indicate its overall relationship to the other system features. The effect of this diagram is to shed further
light on what the information system is expected to do.
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