Not necessarily. One can use tabling (memoization) to prevent that. Also sometimes reordering clauses in the body of a rule is enough to avoid infinite runtime

Not necessarily. One can use tabling (memoization) to prevent that. Also sometimes reordering clauses in the body of a rule is enough to avoid infinite runtime. Datalog (or SQL + recursive CTE) don't have this problem. Mozart/Oz or Alice allow to specify the search strategy.