Variables in technical rules

You can define variables in the condition part of a technical rule and use it subsequently.

when
 {
    ?x: Fish(color==yellow; type==angel);
 }
then
 {
    retract ?x;
    insert Fish(yellow, shark);
 }

The presence of the ?x variable at the beginning of the condition serves as a marker, which identifies any object that matches this condition. You can then refer to the matched object in other conditions or in the action part of the rule. Consequently, when the first action asks for the removal of the object referenced by the ?x rule variable, the yellow angel fish object is removed from the set of objects provided to the rule engine for execution.