Chang-ai Sun

Modeling and managing the variability of Web service-based systems

Web service-based systems are built orchestrating loosely coupled, standardized, and internetworked programs. If on the one hand, Web services address the interoperability issues of modern information systems, on the other hand, they enable the development of software systems on the basis of reuse, greatly limiting the necessity for reimplementation. Techniques and methodologies to gain the maximum from this emerging computing paradigm are in great need. In particular, a way to explicitly model and manage variability would greatly facilitate the creation and customization of Web service-based systems. By variability we mean the ability of a software system to be extended, changed, customized or configured for use in a specific context. We present a framework and related tool suite for modeling and managing the variability of Web service-based systems for design and run-time, respectively. It is an extension of the COVAMOF framework for the variability management of software product families, which was developed at the University of Groningen. Among the novelties and advantages of the approach are the full modeling of variability via UML diagrams, the run-time support, and the low involvement of the user. All of which leads to a great deal of automation in the management of all kinds of variability.

Transaction Management in Service-Oriented Systems: Requirements and a Proposal

Service-Oriented Computing (SOC) is becoming the mainstream development paradigm of applications over the Internet, taking advantage of remote independent functionalities. The cornerstone of SOCs success lies in the potential advantage of composing services on the fly. When the control over the communication and the elements of the information system is low, developing solid systems is challenging. In particular, developing reliable web service compositions usually requires the integration of both composition languages, such as the Business Process Execution Language (BPEL), and of coordination protocols, such as WS-AtomicTransaction and WS-BusinessActivity. Unfortunately, the composition and coordination of web services currently have separate languages and specifications. The goal of this paper is twofold. First, we identify the major requirements of transaction management in Service-oriented systems and survey the relevant standards. Second, we propose a semiautomatic approach to integrate BPEL specifications and web service coordination protocols, that is, implementing transaction management within service composition processes, and thus overcoming the limitations of current technologies.

A Metamorphic Relation-Based Approach to Testing Web Services Without Oracles

Service Oriented Architecture SOA has become a major application development paradigm. As a basic unit of SOA applications, Web services significantly affect the quality of the applications constructed from them. In the context of SOA, the specification and implementation of Web services are completely separated. The lack of source code and the restricted control of Web services limit the testability of Web services, and make the oracle problem prominent. In this context, can one alleviate the test oracle problem, or effectively and efficiently test such Web services even without oracles? It is an important issue which has not been yet adequately addressed. To address the challenge of testing Web services, the authors propose a metamorphic relation-based approach to testing Web services without oracles. The proposed approach leverages so-called metamorphic relations to generate test cases and evaluate test results. To make the proposed approach practical and effective, the authors proposed a framework taking into account the unique features of SOA, and developed a prototype which partially automates the framework. Three case studies are conducted to validate the feasibility and effectiveness of the proposed approach. The work presented in the paper not only alleviates the test oracle problem of testing Web services, but also delivers an effective and efficient test technique without oracles.

Metamorphic Testing for Web Services: Framework and a Case Study

Service Oriented Architecture (SOA) has become a major application development paradigm. As a basic unit of SOA applications, Web services significantly affect the quality of the applications constructed from them. Since the development and consumption of Web services are completely separated under SOA environment, the consumers are normally provided with limited knowledge of the services and thus have little information about test oracles. The lack of source code and the restricted control of Web services limit the testability of Web services. To address the prominent oracle problem when testing Web services, we propose a metamorphic testing framework for Web services taking into account the unique features of SOA. We conduct a case study where the new metamorphic testing framework is employed to test a Web service that implements the electronic payment. The results of case study show the feasibility of the framework for web services, and also the efficiency of metamorphic testing. The work presented in the paper alleviates the test oracle problem when testing Web services under SOA.

Towards Variable Service Compositions Using VxBPEL

The Business Process Execution Language (BPEL) is a widely recognized executable language supporting the specification of process-oriented service compositions. However, the language is limited in addressing variable requirements in the description of business processes. We propose to construct variable and maintainable Web services compositions with VxBPEL, an extension to BPEL we developed to define variability in business process specification. We present the main concepts of VxBPEL and show how to achieve better adaptation and variability maintenance of service compositions, which is particularly desired in the context of dynamically changing business goals and processes.

Requirements and Evaluation of Protocols and Tools for Transaction Management in Service Centric Systems

As service centric (SC) systems are being increasingly adopted, new challenges and possibilities emerge. Business processes are now able to execute seamlessly across organizations and to coordinate the interaction of loosely coupled services. Often it is necessary to have transactionality for a set of business operations, but the loosely nature of such systems calls for techniques and principles that go beyond traditional ACID transactions. By analyzing existing service composition languages, tools, and needs on a classical example, we provide requirements for transactionality in service centric systems and indications for developing SC systems transactionally capable.

Automated Testing of WS-BPEL Service Compositions: A Scenario-Oriented Approach

Nowadays, service oriented architecture (SOA) has become one mainstream paradigm for developing distributed applications. As the basic unit in SOA, web services can be composed to construct complex applications. The quality of web services and their compositions is critical to the success of SOA applications. Testing, as a major quality assurance technique, is confronted with new challenges in the context of service compositions. In this paper, we propose a scenario-oriented testing approach that can automatically generate test cases for service compositions. Our approach is particularly focused on the service compositions specified by Business Process Execution Language for web services (WS-BPEL), a widely recognized executable service composition language. In the approach, a WS-BPEL service composition is first abstracted into a graph model; test scenarios are then derived from the model; finally, test cases are generated according to different scenarios. We also developed a prototype tool implementing the proposed approach, and an empirical study was conducted to demonstrate the applicability and effectiveness of our approach. The experimental results show that the automatic scenario-oriented testing approach is effective in detecting many types of faults seeded in the service compositions.

Scenario-Oriented Testing for Web Service Compositions Using BPEL

Applications are increasingly constructed by orchestrating Web services. Ensuring the reliability of such loosely coupled service compositions is a challenging task. In this paper, we propose an automatic scenario-oriented testing approach for service compositions specified by Business Process Execution Language (BPEL). In our approach, an abstract test model (BGM) is first defined to represent the control flows of BPEL specifications, then test scenarios are derived from the BGM with respect to the given coverage criteria, finally test data are generated to drive the execution of resulting test scenarios. A case study is conducted to demonstrate how our approach can be applied to complex real-life service compositions and the experimental results validate the effectiveness of our approach.

Distribution-Aware Mutation Analysis

Mutation analysis is widely employed to evaluate the effectiveness of various software testing techniques. In most situations, mutation operators are uniformly applied to the original programs, while the faults tend to be clustered in practice. This may result in the inappropriate simulation of faults, and thus cannot deliver the reliable evaluation results. To overcome this, we propose a distribution-aware mutation analysis technique and conducted empirical studies to investigate the impact of the mutation distribution on the effectiveness evaluation of testing techniques. As an illustration, we select the commonly practiced random testing technique and two versions of dynamic random testing techniques and apply them to testing Web services. Results of empirical studies suggest that the mutation distribution significantly affects the evaluation results. This observation further indicates that the effectiveness of testing techniques previously evaluated with the uniform mutation analysis needs further realignments.

ValySeC: A Variability Analysis Tool for Service Compositions Using VxBPEL

Nowadays applications are increasingly developed based on remote Web services and service composition has become a powerful novel development paradigm. Due to the fact that such applications in the context of Internet are deployed and executed in an open and dynamic environment, adaptability is one of the crucial requirements for developing such applications. In our previous work, we presented a variability-based approach to address the adaptability issue of service compositions, and developed the VxBPEL, an extension of BPEL with respect to variability. This paper presents a variability analysis tool for variability-based adaptive service compositions called ValySeC. ValySeC extracts the variation from service compositions specified using VxBPEL and provides a variation view. With the view, the designer can better understand variation points and the possible instances, and efficiently maintain the variation within service compositions. The paper presents the design and implementation of ValySeC using a case study to handle service compositions with variations to illustrate the main concepts.