Separation of concerns is a basic engineering principle that is often applied in object-oriented analysis and design by dissociating functional aspects (business objects) from non-functional ones, such as persistency, fault-tolerance and so on. The Unified Modeling Language (UML) then gives the designer a rich, but somehow disorganized, set of views on her model as well as many features, such as design pattern occurrences, stereotypes or tag values to add non-functional annotations to a model. In this paper, we explore a possibility to organize all of these features around the central notions of (1) quality of service contracts (for specifying non-functional properties a la QML) and (2) aspects for describing how they can be implemented. We propose to model contracts in UML with a small set of stereotypes, and to represent aspects a bit like design pattern occurrences, that is using parameterized collaborations equipped with transformation rules expressed with meta-level OCL2.