Abstract. To be able to build systems by composing a variety of components dynamically, adding and removing as required, is desirable. Unfortunately systems with evolving architectures are prone to behaving in a surprising manner. In this paper we show how it is possible to generate a snapshot of the structure of a running application, and how this can be combined with behavioural specifications for components to check compatability and adherence to system properties. By modelling both the structure and the behaviour, before altering an existing system, we show how dynamic compositional systems may be put together in a predictable manner.