System Development

11.4 Graphical System Representation

There are several various methods for representing computer systems.

11.4.1 Data Flow Diagrams

This type of representation is concerned with how data moves through a system not with such details as what type of data storage is used.

	Source or destination of data external to the system.
	An operation on data which transforms it.
	Any stored data without reference to the physical method of storage.
	This represents the movement of data between any of the above.

Conventions

1. Data flows may not go directly to and from data stores and entities.
2. Data flows must be labelled to indicate what data is been transferred.

11.4.2 System Flow Charts

A systems flow chart shows an overview of the whole system. In particular it represents:

• Tasks to be carried out.
• The hardware devices.
• The inputs, outputs and storage media.
• The files.

	Input/Output
	Keyboard Input
	Process
	Manual Operation
	Sort
	Off Page Connector
	Online Storage
	Magnetic Tape
	Disk Storage
	Visual Display
	Written or Printed Document

Example

Data validation of mail order forms.

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