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Reading a State Diagram — Microwave Oven

publish date: 2026/06/08 10:49:38.067354 UTC

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The diagram below shows the state diagram for a simple microwave oven control system.

Waiting do: display time Full power Half power Full power do: set power = 600 Half power Timer Half power do: set power = 300 Full power Timer Set time do: get number exit: set time Number Door closed Door open Disabled do: display 'Waiting' Door closed Enabled do: display 'Ready' Start Operation do: operate oven Door open Cancel Waiting do: display time

According to this state diagram, what happens when the door is opened while the oven is in the Set time state?

Correct Answer

The oven transitions to the Disabled state

Explanation

According to the state diagram, when the door is opened while the oven is in the Set time state, the system transitions to the Disabled state (do: display 'Waiting'). This is a safety requirement — the oven must not operate when the door is open. The Disabled state shows 'Waiting' on the display, and the system only moves to Enabled once the door is closed again.

Reference

Software Engineering, Ian Sommerville, 10th edition

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