Traditionally system design has been made from a black box/functionality only perspective which forces the developer to concentrate on how the functionality can be decomposed and recomposed into so called components. While this technique is well established and well known it does suffer fromsome drawbacks; namely that the systems produced can often be forced into certain, incompatible architectures, difficult to maintain or reuse and the code itself difficult to debug. Now that ideas such as the OMG's Model Based Architecture (MDA) or Model Based Engineering (MBE) and the ubiquitous modelling language UML are being used (allegedly) and desired we face a number of challenges to existing techniques.