Monday, April 13, 2009

The Data Flow Diagam

The first step is to draw a data flow diagram (DFD). The DFD was-first developed by Larry  Constantine as a way of expressing system requirements  in a graphical form; this led to a modular design.

A DFD, also known as a "bubble chart,’’ has the purpose of clarifying system requirements and identifying major transformations that will be­ come programs in system design, So it is the starting point of the design phase that functionally decomposes the requirements specifications down to the lowest level of detail. 

A DFD consists of a series of bubbles joined by lines, The bubbles represent data transformations and the lines represent data flows in the system. The system takes orders from the customer (bookstore, libaray, etc.), checks them against an index (file) listing the books available, verifies. customer credit through a credit information file, and authorizes shipment with an invoice.

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