Session types for orchestration charts

We present a novel approach for the sound orchestration of services. It is based on Orcharts and Typecharts: a service orchestra- tion language and an associated behavioural typing language. Sessions play a pivotal role in this approach. Orcharts (orchestration charts) de- fine session based services and Typecharts provide for session types with complex interaction patterns that generalise the request/response inter- action paradigm. We provide an algorithm for deciding behavioural well typedeness. We claim that well typed service configurations have the soudness property, i.e., any session that can be initiated in a well typed configuration has its requestor and provider behave in mutual confor- mance and potentially reach service completion.