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

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FRAME-BASED EXPERT SYSTEMS
Figure 5.8
The class Action Data and WHEN CHANGED methods
number of the currently selected instance of the class Request to the attribute
Current Request Number, which is used as a reference point. The FIND command
uses the number stored in Current Request Number to determine the next request
in the list. The LIMIT 1 command tells Level5 Object to find the first instance
that matches the search condition. The WHERE clause
WHERE Request Number OF Request > Current Request Number
locates the first instance of the class Request whose number is greater than the
value of Current Request Number. The request list is maintained in increasing
order to ensure that the proper instance is retrieved. If, for example, the current
instance number is 6, then the FIND command will retrieve the instance with
the number 7.
Let us now consider the class Request and its instances represented in Figure
5.9. The instances, Request 1 and Request 2, have the same attributes as the class
Request, but each instance holds specific values for these attributes. To show the
attribute values on the input display, we have to create value-boxes (display
items that show data) and then attach these value-boxes to the appropriate
attributes. When we run the application, the value-boxes show the attribute