The aim of this paper is to show how the Model Driven Architecture (MDA) can be used in relation with component based software engineer- ing. A software component only exhibits its provided or required interfaces, hence defining basic contracts between components allowing one to properly wire them. These contractually specified interfaces should go well beyond mere syntactic aspects: they should also involve functional, synchronization and Quality of Service (QoS) aspects. In large, mission-critical component based systems, it is also particularly important to be able to explicitly relate the QoS contracts attached to provided interfaces with the QoS contracts ob- tained from required interfaces. We thus introduce a QoS contract model (called QoSCL for QoS Constraint Language), allowing QoS contracts andtheir dependencies to be modeled in a UML2.0 modeling environment.