AI - a Guide to Intelligent Systems.pdf - Member of EEPIS

METHODS AND DEMONS
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Figure 5.7
Input display for the request selection
The input display for the request selection is shown in Figure 5.7. The data on
the display change depending on which business is selected.
The class Action Data, shown in Figure 5.8, is used to control the input display.
The user can move to the next, previous, first or last request in the list of requests
and examine the business data. The WHEN CHANGED methods here allow us to
advance through a list of requests. Note that all attributes in Figure 5.8 are
declared as simple [S]. Simple attributes can assume either a value of TRUE or
FALSE. Let us examine the WHEN CHANGED method attached to the attribute
Goto Next.
How does this method work?
In Level5 Object, any method begins with the reserved words WHEN CHANGED
or WHEN NEEDED, which are followed by the reserved word BEGIN and a series
of commands to be executed. The reserved word END completes a method. To
refer to a particular attribute in a method, we must specify the class name as well
as the attribute name. The syntax is:
OF
For example, the statement Goto Next OF Action Data refers to the attribute Goto
Next of the class Action Data.
The Next pushbutton on the input display is attached to the attribute Goto
Next of the class Action Data. When we select this pushbutton at run time, the
attribute Goto Next receives a value of TRUE, causing the WHEN CHANGED
method attached to it to execute. The method’s first command assigns the