MBE (Model-Based Engineering) proposes to develop software by taking advantage of models, in contrast to traditional code-centric development approaches. If models play a central role in development, model properties must be formulated and checked early on the modeling level, not late on the implementation level. We discuss how to validate and verify model properties in the context of modeling languages like the UML (Unified Modeling Language) combined with textual restrictions formulated in the OCL (Object Constraint Language).