flex Expert System Toolkit - LPIS

7. Knowledge Specification Language 88
Terminating The Engine
flex toolkit
Termination conditions may be set for a particular ruleset using the KSL
keywords
terminate when
followed by some conditions. This provides an alternative way of stopping
the flex program: without termination conditions the forward chaining
engine stops when no more rules can be fired.
Examples
Selecting Rules
ruleset example_set4
contains all rules ;
terminate when condition1 and condition2 .
This specifies that the forward chaining engine will stop when both
condition1 and condition2 are satisfied (even if there are still some
rules which could be fired).
ruleset pack_shopping
contains pack_small_items, pack_large_items ;
terminate when the shopping is empty .
This specifies that the forward chaining engine will stop when the value of
shopping becomes empty.
Normally flex will consider each rule in the order specified in the ruleset.
However, a number of alternative rule selection criteria may be applied
instead, using the KSL keywords
select rule using.
The default rule selection is first come first served, which
considers rules in the order in which they are given and fires the first rule
whose conditions are satisfied.
ruleset example_set5
contains all rules ;
select rule using first come first served .
The rule selected for each cycle is the first rule in the agenda whose
conditions are satisfied. This is the default for selecting rules and is
equivalent to omitting any rule selection criteria.
Rules may be selected using conflict resolution. In this case an
attempt is always made to use the “best” rule according to the scoring
system built into the rules. Each rule should have a score associated with it,
and the conflict resolution system then fires the rule whose conditions are