Xiangpeng Zhao

Towards the theoretical foundation of choreography

With the growth of interest on the web services, people pay increasinglyattention to the choreography, that is, to describe collaborations ofparticipants in accomplishing a common business goal from a globalviewpoint. In this paper, based on a simple choreography language and arole-oriented process language, we study some fundamental issues relatedto choreography, especially those related to implementation, includingsemantics, projection and natural projection, dominant role in choices anditerations, etc. We propose the concept of dominant role and somenovel languages structures related to it. The study reveals some cluesabout the language, the semantics, the specification and theimplementation of choreography.

Towards the Semantics and Verification of BPEL4WS

In this paper, we discuss the semantics of BPEL4WS language which is a de facto standard for specifying and execution workflow specification for web service composition and orchestration. We propose a language @m-BPEL that includes most primitive and structured activities of BPEL4WS, and define its semantics. As the Timed Automata (TA) is powerful in designing real-time models with multiple clocks and has well developed automatic tool support, we define a map from @m-BPEL into composable TA. Therefore, the properties we want to check can be verified in TA network correspondingly. Furthermore, we prove that the mapping from @m-BPEL to TA is a simulation, which means that the TA network simulates correctly the corresponding @m-BPEL specification. The case study with model checker Uppaal shows that our method is effective, and a Java supporting tool based on Uppaal model checker engine has been developed.

Semantics of BPEL4WS-Like fault and compensation handling

BPEL4WS is one of the most important business process modelling languages. One distinct feature of it is the fully programmable fault and compensation handling mechanism, which allows the user to specify the compensation behaviors of processes in application-specific manners. In this paper, we present a formal operational semantics to a simplified version of BPEL4WS, with some important concepts related to fault and compensation handling proposed and discussed, especially, the compensation closure and the compensation context. We also discuss some insights into the BPEL4WS language and its implementation obtained from this study.

A Formal Model forWeb Service Choreography Description Language (WS-CDL)

We propose a language CDL as a formal model of simplified WS-CDL. The operational semantics of CDL is given, and static validation and verification of choreographies is studied. Some properties of the proposed model are verified using the SPIN model-checker, which illustrates the potential usage and benefits of the formal model

Model checking dynamic UML consistency

UML is widely accepted and extensively used in software modeling. However, using different diagrams to model different aspects of a system brings the risk of inconsistency among diagrams. In this paper, we investigate an approach to check the consistency between the sequence diagrams and statechart diagrams using the SPIN model checker. To deal with the hierarchy structure of statechart diagrams, we propose a formalism called Split Automata, a variant of automata, which is helpful to bridge the statechart diagrams to SPIN efficiently. Compared with the existing work on model checking UML which do not have formal verification for their translation from UML to the model checker, we formally define the semantics and prove that the automatically translated model (i.e. Split Automata) does simulate the UML model. In this way, we can guarantee that the translated model does represent the original model.

Enforcing Constraints on Life Cycles of Business Artifacts

Artifact-centric business process models allow to describe artifacts (data objects) and their life cycles, which allow designers to focus on individual artifact in business processes, thus simplifies the design and analysis of business process model. However, this feature is a double-edged sword. The description of the relationships between artifacts becomes a new and nontrivial problem. It is better that the associations among business artifacts are specified at a high level as logical assertions. We think taking business constraints as complements of artifact-centric business operational model is an useful idea. Based on this consideration,in this paper, we propose an approach which combines both the declarative way and the procedural way in the construction of business processes. This flexibility can help designers to separate the parts of a business process that are more likely to change from those that are less likely to change. We propose a language TiLE to specify business constraints, and give complexity results on the satisfiability of TiLE. Moreover, we discussed how to enforce the constraints at run-time.

Type checking choreography description language

The Web Services Choreography Description Language (WS-CDL) is a W3C specification developed for the description of peer-to-peer collaborations of participants from a global viewpoint. Currently WS-CDL has no rigorous static type checking. We believe that introducing a type system will exclude many design and description errors, and ensure desirable properties of the choreography specifications. In this paper, we took a core language CDL, which covers most of the important features of the WS-CDL, and is more convenient for the study. We developed the abstract syntax and operational semantics of CDL, and defined a collection of rules which can be used to check if choreography is well-typed. Moreover, we also proved some type safety theorems for CDL in the sense that well-typed choreography cannot get stuck. We show how the use of type information can allow us to gain confidence in the correctness of choreography.

A Formal Model for Channel Passing in Web Service Composition

Despite the importance for expressing location mobility and dynamic composition, channel passing has almost been ignored in the formal work on Web service composition. One important problem here is to ensure that each service in a composition can always get sufficient and correct channels for completing their collaborative work. To support reasoning and verification of those properties of service compositions, in this paper we propose a pair of formal languages that support channel passing on both global and local levels, together with their semantics. Also we present a top-down design methodology that generates local-level processes from global description, and prove that the generated processes must be deadlock-free under the sufficient conditions we proposed.

Patterns with Algebraic Properties in BPEL0

In the paper, we proposed a language called BPEL0 with its formal semantics as the foundations of WSBPEL. In this paper, we follow the way Van der Aalst proposed on pattern analysis in workflow languages (2003), and present the patterns for BPEL0. Moreover, the expressiveness of BPEL0 is also embodied by means of putting these patterns in the program environment composed of other programming operators. Those properties about the patterns with its environment are captured by the algebraic laws, which can be proven in the framework of BPEL0 semantic domain.

Global-to-local approach to rigorously developing distributed system with exception handling

Cooperative distributed system covers a wide range of applications such as the systems for industrial controlling and business-to-business trading, which are usually safety-critical. Coordinated exception handling (CEH) refers to exception handling in the cooperative distributed systems, where exceptions raised on a peer should be dealt with by all relevant peers in a consistent manner. Some CEH algorithms have been proposed. A crucial problem in using these algorithms is how to develop the peers which are guaranteed coherent in both normal execution and exceptional execution. Straightforward testing or model checking is very expensive. In this paper, we propose an effective way to rigorously develop the systems with correct CEH behavior. Firstly, we formalize the CEH algorithm by proposing a Peer Process Language to precisely describe the distributed systems and their operational semantics. Then we dig out a set of syntactic conditions, and prove its sufficiency for system coherence. Finally, we propose a global-to-local approach, including a language describing the distributed systems from a global perspective and a projection algorithm, for developing the systems. Given a well-formed global description, a set of peers can be generated automatically. We prove the system composed of these peers satisfies the conditions, that is, it is always coherent and correct for CEH.