In a UML model, different aspects of a system are covered by different types of diagrams and this bears the risk that an overall system specification becomes barely tractable by the designer. When the model grows, it is likely that the architectural integrity will be compromised by extensions and bug-fixing operations. Hence, it is important to provide means to help designers to search in big models for particular instances of some variable schema of UML models (design patterns) they construct. This can help them both to find potential problems in the architecture design and to ensure that intended architectural choices had not been broken by mistake. In this paper we propose a rule-based method to find matches of design patterns into a UML model. The method is general enough to tackle most patterns and antipatterns.