Prolog is frequently used in implementing natural language parsers or generators based on unification based grammars. This is because Prolog is also based on unification, and therefore has a declarative feature. One important characteristic of unification cu-Prolog adopts constraint unification instead of based grammar is also a declarative grammar formalthe normal Prolog unification. In cu-Prolog, con- ization [11]. However, Prolog does not have sufficient power of straints in terms of user defined predicates can be expressing constraints because it executes every parts directly added to the program clauses. .
