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 orchestration language and an associated behavioural typing language. Sessions play a pivotal role in this approach. Orcharts (orchestration charts) define session based services and Typecharts provide for session types with complex interaction patterns that generalise the request/response interaction 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 conformance and potentially reach service completion.