To ensure the quality of an information system we must guarantee the correctness of the conceptual schema that represents the knowledge about its domain. The high expressivity of UML schemas annotated with textual OCL constraints enforces the need for automated reasoning techniques. These techniques should be both terminating and complete to be effectively used in practice. In this paper we identify an expressive fragment of the OCL language that ensures these properties. In this way, we overcome the limitations of current techniques when reasoning on such a fragment. As a consequence, we also have that Description Logics can be appropriately used to reason on UML conceptual schemas with arbitrary OCL constraints. We also show how current tools based on different approaches can be used to reason on conceptual schemas enriched with (a decidable fragment of) OCL constraints.