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7. Knowledge Specification Language 101<br />
displayed.<br />
question choose_colours<br />
Select your colours ;<br />
choose some of red, green, yellow, blue, black,<br />
white.<br />
This is exactly equivalent to:<br />
question choose_colours<br />
Select your colours ;<br />
choose from red, green, yellow, blue, black, white.<br />
Alternatively, a group name may be given for the menu items, e.g.<br />
group colours<br />
red, green, yellow, blue, black, white.<br />
question choose_a_colour<br />
Select a colour ;<br />
choose one of colours.<br />
To actually invoke a question, use the KSL keyword ask in a directive.<br />
For example, the colours question given above will be invoked by the<br />
following <strong>flex</strong> relation.<br />
relation get_colour( C )<br />
if ask choose_a_colour<br />
and C is choose_a_colour .<br />
The Prolog query<br />
?- get_colour( C ).<br />
will display a standard menu dialog (its actual appearance will depend on the<br />
particular implementation of <strong>flex</strong> that you are using), and the user’s choice<br />
will be stored in the <strong>flex</strong> global variable choose_a_colour and returned<br />
as the value of the Prolog variable C.<br />
Note that to define get_colour/1 as an equivalent action, we would need<br />
to use the KSL check that construct.<br />
action get_colour( C ) ;<br />
do ask choose_a_colour<br />
and check that C is choose_a_colour .<br />
Explanations<br />
<strong>flex</strong> toolkit<br />
The question dialog will normally contain a button labelled Explain, which<br />
allows for explanations to be attached to questions. The user may click the<br />
Explain button and the <strong>flex</strong> programmer may provide text to be displayed<br />
at this point (using the KSL keyword because), as an explanation of why
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