
We study the succinctness of monadic secondorder logic and a variety of monadic fixed point logics on trees. All these languages are known to have the same expressive power on trees, but some can express the same queries much more succinctly than others. For example, we show that, under some complexity theoretic assumption, monadic secondorder logic is nonelementarily more succinct than monadic least fixed point logic, which in turn is nonelementarily more succinct than monadic datalog.
Succinctness of the languages is closely related to the combined and parameterized complexity of query evaluation for these languages.
© 20022003 Kurt Gödel Society, Norbert Preining. 
20030604
 