Geguang Pu

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.

Building a web thesaurus from web link structure

Thesaurus has been widely used in many applications, including information retrieval, natural language processing, and question answering. In this paper, we propose a novel approach to automatically constructing a domain-specific thesaurus from the Web using link structure information. The proposed approach is able to identify new terms and reflect the latest relationship between terms as the Web evolves. First, a set of high quality and representative websites of a specific domain is selected. After filtering out navigational links, link analysis is applied to each website to obtain its content structure. Finally, the thesaurus is constructed by merging the content structures of the selected websites. The experimental results on automatic query expansion based on our constructed thesaurus show 20% improvement in search precision compared to the baseline.

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

Modeling and Verifying Web Services Choreography Using Process Algebra

The Web Services Choreography Description Language (WS-CDL) is a newly developed specification for Web services composition to describe the observable behavior across multiple participants from a global perspective. However, this specification does not provide a formal semantics, whose informal description can lead to ambiguous understanding and different implementations. Hence, it causes difficulties for the engineering community to analyze the business behavior and ensure the correctness. In this paper, we present the semantics of WS-CDL in terms of process algebra CSP which has great advantages in designing and verifying concurrent processes. Therefore, all the properties we want to check within a WS-CDL document can be verified automatically in the CSP framework correspondingly. In addition, the exception and compensation handling mechanism, an important concept of long running transactions, is demonstrated clearly through our formalization work.

Tool Support for BPEL Verification in ActiveBPEL Engine

The BPEL is designed for integrating and orchestrating Web services and it provides the profound solution to model business process relying on Web service platform. ActiveBPEL is a commercial-grade open source implementation engine for BPEL. In this paper, we describe the work on tool support for the BPEL verification in ActiveBPEL. We implement the algorithm of the mapping from BPEL to timed automata, and integrate it into the ActiveBPEL. By using model checker UPPAAL engine, ActiveBPEL is enhanced and can verify the BPEL properties, such as deadlock and reachability. Moreover, those timed properties of BPEL specification can be checked in our framework as well. Some case studies are presented to show the usage of verification functionality in ActiveBPEL.

Towards the Semantics for Web Service Choreography Description Language

A choreography is a multi-part contract which describes peer to peer collaboration of services regardless of any specific programming language or supporting platform. WS-CDL, issued from W3C, is the first language for describing choreography. In this paper, we propose a language CDL0 to capture the important features of WS-CDL, including choreography composition, compensation and exception handling. An adjunctive concept role reference is introduced with the aim of distinguishing multiple participants which provide the same kind of service within a choreography model. The semantics is given by an operational approach to provide a formal base for the choreography language. We believe this formalism work helps to clear ambiguous points in the WS-CDL specification and promote the usage of choreography languages.

Model-Based Methods for Linking Web Service Choreography and Orchestration

In recent years, many Web service composition languages have been proposed. Web service choreography describes collaboration protocols of cooperating Web service participants from a global view. Web service orchestration describes collaboration of the Web services in predefined patterns based on local decision about their interactions with one another at the message/execution level. In this work, we present model-based methods to close the gap between the two views. Building on the strength of model checking techniques, Web service choreography and orchestration are verified against temporal properties or against each other (to show that they are consistent). Specialized optimization techniques are developed to handle large Web service models. Furthermore, we propose a method to mechanically synthesize a prototype Web service orchestration from choreography, by repairing the choreography if necessary and projecting relevant behaviors to each service provider.

Guided, stochastic model-based GUI testing of Android apps

Mobile apps are ubiquitous, operate in complex environments and are developed under the time-to-market pressure. Ensuring their correctness and reliability thus becomes an important challenge. This paper introduces Stoat, a novel guided approach to perform stochastic model-based testing on Android apps. Stoat operates in two phases: (1) Given an app as input, it uses dynamic analysis enhanced by a weighted UI exploration strategy and static analysis to reverse engineer a stochastic model of the apps GUI interactions; and (2) it adapts Gibbs sampling to iteratively mutate/refine the stochastic model and guides test generation from the mutated models toward achieving high code and model coverage and exhibiting diverse sequences. During testing, system-level events are randomly injected to further enhance the testing effectiveness. Stoat was evaluated on 93 open-source apps. The results show (1) the models produced by Stoat cover 17~31% more code than those by existing modeling tools; (2) Stoat detects 3X more unique crashes than two state-of-the-art testing tools, Monkey and Sapienz. Furthermore, Stoat tested 1661 most popular Google Play apps, and detected 2110 previously unknown and unique crashes. So far, 43 developers have responded that they are investigating our reports. 20 of reported crashes have been confirmed, and 8 already fixed.

Looking into Compensable Transactions

Transaction is a lasting debatable issue, no matter in database systems or in the new paradigm of web services. Particularly, in the context of service oriented computing, business transactions usually require long periods of time to complete. In case of failure, the traditional approaches, e.g., rollback, are not applicable to handle errors during long running transactions. Instead, compensation is suggested to be an error recovery mechanism. Hence, a business transaction is programmed as a composition of a set of compensable transactions. Sequence and parallel are two standard primitives to put compensable transactions together into a bigger compensable one. Besides, there are other useful compositional constructs, such as speculative choice, exception handling, alternative forwarding, and programmable compensation. These constructs cannot only improve the responsiveness to environment but also enhance the capability for dealing with errors. In this paper, we introduce a transactional calculus in which compensable transactions can be composed in a variety of ways. It is equipped with a trace model which is carefully presented to provide a clear meaning for each transactional construct. In addition, algebraic properties are investigated by giving corresponding equational laws.