  The growing complexity of software systems as well as changing conditions in
their operating environment demand systems that are more flexible, adaptive and
dependable. The service-oriented computing paradigm is in widespread use to
support such adaptive systems, and, in many domains, adaptations may occur
dynamically and in real time. In addition, services from heterogeneous,
possibly unknown sources may be used. This motivates a need to ensure the
correct behaviour of the adapted systems, and its continuing compliance to time
bounds and other QoS properties. The complexity of dynamic adaptation (DA) is
significant, but currently not well understood or formally specified. This
paper elaborates a well-founded model and theory of DA, introducing formalisms
written using COWS. The model is evaluated for reliability and responsiveness
properties with the model checker CMC.
