Thursday 1 May 2014

Flowcharts

To understand what a system flowchart is, it helps to know that the most basic definition of a system is: a connection of parts that does something useful.

What is a system flowchart?

System flowcharts are a way of displaying how data flows in a system and how decisions are made to control events.
To illustrate this, symbols are used. They are connected together to show what happens to data and where it goes. The basic ones include:
Decisions (yes, no) are represented by a diamond. Processes (something that happens) are represented by a rectangle. Inputs and outputs are represented by a parallelagram. An arrow represents the data flow, indicating the direction of data flow.
Symbols used in flow charts
Note that system flow charts are very similar to data flow charts. Data flow charts do not include decisions, they just show the path that data takes, where it is held, processed, and then output.

Using system flowchart ideas

This system flowchart is a diagram for a 'cruise control' for a car. The cruise control keeps the car at a steady speed that has been set by the driver.
The speed sensor detects the speed of the car. If the car is too fast, less fuel is provided to the engine and teh flow chart returns to the start. If it is not too fast, is it too slow? If it is too slow, more fuel is sent to the engine and the flow chart returns to the start. If it is not too slow, the flow chart returns to the start.
A system flowchart for cruise control on a car
The flowchart shows what the outcome is if the car is going too fast or too slow. The system is designed to add fuel, or take it away and so keep the car's speed constant. The output (the car's new speed) is then fed back into the system via the speed sensor.
Other examples of uses for system diagrams include:
  • aircraft control
  • central heating
  • automatic washing machines
  • booking systems for airlines

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