flex Expert System Toolkit - LPIS

7. Knowledge Specification Language 89
satisfied with the highest score.
ruleset example_set6
contains all rules ;
select rule using conflict resolution .
Note that there is a high cost to using conflict resolution since every rule
must be tested before the highest score is known.
An adaptation of conflict resolution is to set a threshold value, so that the
first rule whose conditions are satisfied and whose score is greater than the
threshold value will be fired. This reduces the search somewhat.
ruleset example_set7
contains all rules ;
select rule using conflict resolution
with threshold 7 .
The rules are selected using the conflict resolution scoring system with a
threshold value (in this example the threshold value is 7).
Finally, the flex programmer may specify a routine which makes a rule
selection from the current agenda.
ruleset example_set8
contains all rules ;
select rule using my_selector .
Here flex will look for a program called my_selector/3 which should be
defined with three arguments:
my_selector( RuleAgenda, RuleConditions, Actions )
where at the time of the call RuleAgenda will be instantiated to a list of the
names of the rules currently in the rule agenda, and RuleConditions and
Actions are variables which my_selector should bind to the conditions
and actions respectively of the required rule. For more information see the
description of the predicates new_rule/5, isa_rule/5 and
forward_chain/5 in the "flex Predicates" chapter of this manual.
Updating The Rule Agenda
Each time a rule is fired, there is the option of updating the rule agenda for
the next cycle of the forward chaining engine. The default is to leave the set
of rules exactly as it is, so that the rules are always considered in the same
order every time. Other options may be specified using the KSL keywords
update ruleset
The options are as follows.
Each time a rule is fired it can be removed from the ruleset. This effectively
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