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We introduce B , a lightweight language for web services orchestration designed around some of WS-BPEL peculiar features like partner links, process termination, message correlation, long-running business transactions and compensation handlers. B formal presentation helps clarifying some ambiguous aspects of the WS-BPEL specification, which have led to engines implementing different semantics and, thus, have undermined portability of WS-BPEL programs over different platforms. We illustrate the main features of B by means of many examples, some of which are also exploited to test and compare the behaviour of three of the most known free WS-BPEL engines.