As I mention in my book we have too much considered SOA as client/server on Web Services. We really need to think variability as a way to enable reuse and avoid the propagation of provider changes to consumers and vice versa. In complement to the approach for variability I describe in my book looking at information variability, service variability and process variability here are two good articles on variability that an architect I work with in a large european bank just sent to me as we are working on these topics together for that bank.
A Taxonomy of Variability Realization Techniques
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