sorry, i used the wrong word "action", instead of "data". take the schema once more to avoid misunderstanding (assume no grouped rows). ------------------------------------------- | CONDITION ------------------------------------------- object type/ | $p : Person ------------------------------------------- snippet/condition | ? ------------------------------------------- explaination text | xxxxxxxxx ------------------------------------------- cell/data | ? ------------------------------------------- it's clear: the condition ("snippet" in my term) can not be empty, and the data ("cell" in my term) can be empty. in my case how should i put the condition, when no field constraint is there? how should i put in the data? an empty invalidates the condition! the case i raised seems trivial. actually it finds many applications as follows. in question comes the rule "otherwise": rule "main" salience 10 when $p : Person(age > 35) then // do something with persons older than 35 System.out.println("hello, " + $p + "!"); end rule "otherwise" when $p : Person() then // ignore other persons, i.e. retract them to avoid memory leaks retract($p); end / Ben