In computational linguistics, we are often interested in developing grammar formalisms declaratively. However, tractability often becomes a problem then. Therefore, we want to argue for the use of constraint logic programming (CLP), and it is yet interesting to note that most logic based natural language systems have not attempted to employ CLP. Our framework and the prototype system UBS combines logic programming with constraint domains (e.g. typed feature structures and finite sets) and constraint techniques (e.g. coroutining).