Precise Modelling of Compensating Business Transactions and its Application to BPEL

We describe the StAC language which can be used to specify the orchestration of activities in long running business transactions. Long running business transactions use compensation to cope with exceptions. StAC supports sequential and parallel behaviour as well as exception and compensation handling. We also show how the B notation may be combined with StAC to specify the data aspects of transactions. The combination of StAC and B provides a rich formal notation which allows for succinct and precise specification of business transactions. BPEL is an industry standard language for specifying business transactions and includes compensation constructs. We show how a substantial subset of BPEL can be mapped to StAC thus demonstrating the expressiveness of StAC and providing a formal semantics for BPEL

On the Expressiveness of Intensional Communication

The expressiveness of communication primitives has been explored in a common framework based on the pi-calculus by considering four features: synchronism (asynchronous vs synchronous), arity (monadic vs polyadic data), communication medium (shared dataspaces vs channel-based), and pattern-matching (binding to a name vs testing name equality). Here pattern-matching is generalised to account for terms with internal structure such as in recent calculi like Spi calculi, Concurrent Pattern Calculus and Psi calculi. This paper explores intensionality upon terms, in particular communication primitives that can match upon both names and structures. By means of possibility/impossibility of encodings, this paper shows that intensionality alone can encode synchronism, arity, communication-medium, and pattern-matching, yet no combination of these without intensionality can encode any intensional language.Comment: In Proceedings EXPRESS/SOS 2014, arXiv:1408.127

Refinement for Probabilistic Systems with Nondeterminism

Before we combine actions and probabilities two very obvious questions should be asked. Firstly, what does "the probability of an action" mean? Secondly, how does probability interact with nondeterminism? Neither question has a single universally agreed upon answer but by considering these questions at the outset we build a novel and hopefully intuitive probabilistic event-based formalism. In previous work we have characterised refinement via the notion of testing. Basically, if one system passes all the tests that another system passes (and maybe more) we say the first system is a refinement of the second. This is, in our view, an important way of characterising refinement, via the question "what sort of refinement should I be using?" We use testing in this paper as the basis for our refinement. We develop tests for probabilistic systems by analogy with the tests developed for non-probabilistic systems. We make sure that our probabilistic tests, when performed on non-probabilistic automata, give us refinement relations which agree with for those non-probabilistic automata. We formalise this property as a vertical refinement.Comment: In Proceedings Refine 2011, arXiv:1106.348