A Calculus for Orchestration of Web Services

We introduce COWS (Calculus for Orchestration of Web Services), a new foundational language for SOC whose design has been influenced by WS-BPEL, the de facto standard language for orchestration of web services. COWS combines in an original way a number of ingredients borrowed from well-known process calculi, e.g. asynchronous communication, polyadic synchronization, pattern matching, protection, delimited receiving and killing activities, while resulting different from any of them. Several examples illustrates COWS peculiarities and show its expressiveness both for modelling imperative and orchestration constructs, e.g. web services, flow graphs, fault and compensation handlers, and for encoding other process and orchestration languages

Towards verification of computation orchestration

Recently, a promising programming model called Orc has been proposed to support a structured way of orchestrating distributed Web Services. Orc is intuitive because it offers concise constructors to manage concurrent communication, time-outs, priorities, failure of Web Services or communication and so forth. The semantics of Orc is precisely defined. However, there is no automatic verification tool available to verify critical properties against Orc programs. Our goal is to verify the orchestration programs (written in Orc language) which invoke web services to achieve certain goals. To investigate this problem and build useful tools, we explore in two directions. Firstly, we define a Timed Automata semantics for the Orc language, which we prove is semantically equivalent to the operational semantics of Orc. Consequently, Timed Automata models are systematically constructed from Orc programs. The practical implication is that existing tool supports for Timed Automata, e.g., Uppaal, can be used to simulate and model check Orc programs. An experimental tool has been implemented to automate this approach. Secondly, we start with encoding the operational semantics of Orc language in Constraint Logic Programming (CLP), which allows a systematic translation from Orc to CLP. Powerful constraint solvers like CLP(R) are then used to prove traditional safety properties and beyond, e.g., reachability, deadlock-freeness, lower or upper bound of a time interval, etc. Counterexamples are generated when properties are not satisfied. Furthermore, the stepwise execution traces can be automatically generated as the simulation steps. The two different approaches give an insight into the verification problem of Web Service orchestration. The Timed Automata approach has its merits in visualized simulation and efficient verification supported by the well developed tools. On the other hand, the CPL approach gives better expressiveness in both modeling and verification. The two approaches complement each other, which gives a complete solution for the simulation and verification of Computation Orchestration

Whoever that likes relatives

In this paper we will deal with some aspects of free relative clauses (FRC) in English, showing that there are certain differences between restrictive relative clauses (RRC) featuring whoever on the one hand and whichever / whatever on the other in terms of both their syntax and their semantics. In particular, we will focus on solving a long-standing puzzle that involves paradigms where the opposite of what the venerable *that-t filter would predict obtains

Verification and Analysis of Web Service Composition

Ph.DDOCTOR OF PHILOSOPH

Coordination models Orc and Reo compared

Orc and Reo are two complementary approaches to the problem of coordinating components or services. On one hand, Orc is highly asynchronous, dynamic, and based on ephemeral connections to services. On the other hand, Reo is based on the interplay between synchronization and mutual exclusion, is more static, and establishes more continuous connections between components or services. The question of how Orc and Reo relate to each other naturally arises. In this paper, we present a detailed comparison of the two models. We demonstrate that embedding non-recursive Orc expressions into Reo connectors is straightforward, whereas recursive Orc expressions require an extension to the Reo model. For the other direction, we argue that embedding Reo into Orc would require, based on expressiveness results of Palamidessi, signifficantly more effort. We conclude with some general observations and comparisons between the two approaches

The computational complexity of QoS measures for orchestrations

The final publication is available at link.springer.comWe consider Web services defined by orchestrations in the Orc language and two natural quality of services measures, the number of outputs and a discrete version of the first response time. We analyse first those subfamilies of finite orchestrations in which the measures are well defined and consider their evaluation in both reliable and probabilistic unreliable environments. On those subfamilies in which the QoS measures are well defined, we consider a set of natural related problems and analyse its computational complexity. In general our results show a clear picture of the difficulty of computing the proposed QoS measures with respect to the expressiveness of the subfamilies of Orc. Only in few cases the problems are solvable in polynomial time pointing out the computational difficulty of evaluating QoS measures even in simplified models.Peer ReviewedPostprint (author's final draft

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

Principles of Security and Trust

This open access book constitutes the proceedings of the 8th International Conference on Principles of Security and Trust, POST 2019, which took place in Prague, Czech Republic, in April 2019, held as part of the European Joint Conference on Theory and Practice of Software, ETAPS 2019. The 10 papers presented in this volume were carefully reviewed and selected from 27 submissions. They deal with theoretical and foundational aspects of security and trust, including on new theoretical results, practical applications of existing foundational ideas, and innovative approaches stimulated by pressing practical problems