ITPEC FE Morning April 2023 Question 62

The greenhouse control system — a state transition diagram suits a system whose behaviour depends on its current state and on incoming events.

A state transition diagram shows the states a system can be in, the events that move it from one state to another and the actions taken on each transition. Control systems are the typical case: the greenhouse controller switches between states such as heating, cooling, ventilating and idle as sensor readings cross thresholds, and what it does next depends on the state it is in.

Answer (b)

Why not others:

• •(a) — calculating a charge from a meter reading is a fixed computation from input to output, with no states to switch between; a processing flow describes it
• •(c) — aggregating inventory at month end and at settlement is scheduled batch processing, driven by the calendar rather than by events changing a state
• •(d) — measuring resource usage and producing a report is data collection and output, again a flow of data with no state-dependent behaviour

Key rule: Use a state transition diagram for event-driven, real-time or control systems; model batch calculation and reporting with a data flow instead.

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