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