One important aspect in the specification of conceptual schemas is the definition of general constraints that cannot be expressed by the predefined constructs provided by conceptual modeling languages. In general this is done by means of general-purpose languages, like OCL. In this paper we propose a new approach to facilitate the definition of such general constraints in UML. More precisely, we define a profile that extends the set of UML predefined constraints with some types of constraints that are used very frequently in conceptual schemas. We also study the application of our ideas to the specification of two real-life applications and we show how results in constraint-related problems may be easily incorporated to our proposal.