flex Expert System Toolkit - LPIS

3. Forward Chaining 33
can give the rule a dynamic score.
rule empty_master_into_slave
if the master is not empty
and
the slave`s contents
> the master`s spare_capacity
then fill_from( master, slave )
score master`s contents plus slave`s contents .
As the contents of the two vessels change, so the weighting of this rule also
changes. We could even give the system a sense of chance by using randomvalued
scores.
Attaching Explanations to Rules
The final part of a production rule in flex involves the attachment of an
optional explanation to rules. This is used to explain why a rule was fired.
The explanation itself can either be some canned text or a pointer to a disk
file accessed at run-time through a file browser.
When explaining the rule either the canned text is displayed on screen or
the user is allowed to browse through the file.
rule 'check status'
if the applicant`s job is officer
and the applicant`s age is greater than 65
then ask_for_grading
because The job grading affects the pension .
The above rule will cause the single line of text The job grading
affects the pension to be displayed on the screen whenever an
explanation is requested.
The latter alternative allows for a more flexible explanation facility. Indeed,
the only purpose of the rule-based system might be as an intelligent link into
the file browsing system. Such applications include the reviewing of
technical manuals, especially medical journals.
rule 'check status'
if the applicant`s job is principal
and the applicant`s age is greater than 65
then check_principal_function
browse file status .
The Forward Chaining Engine
The forward chaining engine is implemented as a Prolog program. The
emphasis of the implementation is placed upon simplicity coupled with great
flexibility, rather than extracting the highest possible performance.
flex toolkit