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Advanced Data Representation and File Organisation: Question 6

Syllabus 13.1

Multiple choice A2 1 mark

A vehicle-tracking app needs, for each vehicle, to store its RegistrationNumber and its current Speed together with a self-contained operation IsSpeeding() that works out. Using only that one vehicle's own stored data. Whether it is currently over the speed limit. The operation must be bundled with the data it acts on, rather than written as a separate function kept apart from the data.

Which composite user-defined data type is most suitable for representing one vehicle?

Choose an answer to check it, then compare with the worked solution below.
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Worked solution

Matching the requirement to a composite data type

The syllabus lists four composite user-defined data types: set, record, and class/object. The requirement here has two parts: (1) group RegistrationNumber and Speed together for one vehicle, and (2) bundle in an operation, IsSpeeding(), that works directly on that vehicle’s own stored data, as part of the same variable.

A record can satisfy the first part. It groups related fields of possibly different types under one identifier, but a record holds data only. It has no mechanism for storing an operation alongside its fields, so IsSpeeding() could not be bundled into it directly.

A class/object satisfies both parts. A class defines both attributes (data fields, such as RegistrationNumber and Speed) and methods (operations, such as IsSpeeding()) together, and an object created from that class carries its own data and can have its methods called directly on it, exactly what the scenario asks for.

CLASS Vehicle
    PRIVATE RegistrationNumber : STRING
    PRIVATE Speed : INTEGER

    PUBLIC FUNCTION IsSpeeding() RETURNS BOOLEAN
        IF Speed > 70 THEN
            RETURN TRUE
        ELSE
            RETURN FALSE
        ENDIF
    ENDFUNCTION
ENDCLASS

Why the other options are wrong

  • A (record): groups data fields together but cannot also hold an operation as part of the same variable. A record has no methods.
  • C (set): a set is an unordered collection of unique values (for example, a set of colours currently in use); it is not designed to model one entity’s data and behaviour together.
  • D (enumerated): an enumerated type defines a fixed list of named constant values (for example, Easy, Medium, Hard); it has no fields and no operations at all.

Final answer

B. A class/object is the correct choice, because it is the only composite type that bundles a single entity’s data attributes together with the operations that act on that data.