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Variables, Parameters, and Rules

Parameters and variables are tightly coupled with rules. A common use of rules is to test whether a variable or parameter has a certain value, and, if so, to take some subsequent action, possibly involving another variable or parameter.

For both parameters and variables, the relationship with rules involves forward chaining. Each can either:

Cause forward chaining to a rule when either receives a value
Receive a value from the consequent of a rule invoked from another variable or parameter that forward chained to the rule.

Forward chaining is the process of invoking a rule when at least one of the conditions in its antecedent is true. Consider the following rule as an example.

Whenever the Tank-volume variable for AUTO-1 obtains the value low from some source, that occurrence causes forward chaining to the antecedent of this rule. The rule's consequent concludes a new value for the auto-needs-gas parameter. When the auto-needs-gas parameter receives a value as the effect of the variable update forward chaining to the rule, it, in turn could cause forward chaining to another rule containing that parameter in its antecedent. For a complete description of forward chaining, see Forward Chaining.

In summary, a new value for a variable or parameter can cause forward chaining to the antecedent of one or more rules.

For variables, the relationship with rules involves both forward chaining and backward chaining, described next.

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