The railway maintenance program decides whether a track section can be reopened after overnight work. The section is available if an engineer has signed it ...
Question 1 Report
The railway maintenance program decides whether a track section can be reopened after overnight work. The section is available if an engineer has signed it off and either the automated sensor test passes or a manual inspection passes. The program stores the three results as Boolean variables. A supervisor wants to use the statement open = signedOff AND (sensorPass OR manualPass). This prevents an unsigned section opening merely because a test result is positive. Consider a section that is signed off, fails the sensor test, but passes manual inspection.
(a) Explain why the OR operation is inside brackets. [2]
(b) When the three values are True, False and True in the order given, state the value of open. [1]
(c) When signedOff is False and both test variables are True, state the value of open. [1]
(d) Explain why the sign-off check is important in this program. [1]
Answer Details
The rule is open = signedOff AND (sensorPass OR manualPass).
- (a) Either test may provide a pass, so
sensorPass OR manualPassis grouped together. [1] The resulting test decision is then combined withsignedOffusingAND. [1] - (b) For signed off True, sensor pass False, manual pass True: False OR True is True, then True AND True is True. The section can open. [1]
- (c) If
signedOffis False, then even if both tests pass, False AND True is False. [1] - (d) The sign-off check ensures that an authorised engineer has approved reopening. [1]
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