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Recently, Web service composition and optimization have received an increasing attention from both academia and industrial community. Most current methods have not paid enough attention to the user specific trust requirement for composite services. However, Trust is an important metric to judge whether a composite service can behave as user expected. In this work, firstly, a multifactor concept of trust of composite service is defined based on the trust of component services, interface compatibility and optimal binding schemes. Secondly, a trustworthy Web service composition and optimization framework called TWSCO is proposed to guarantee the trust of composite service and efficiency of Web service composition process. The interface-matching problem among component services and user preference are considered in TWSCO, which firstly uses component services filter to remove untrusted component services. Secondly, the concrete services, based on interface similarity, are organized as clusters. Thirdly, a composite template among component services is formed at the cluster level to guarantee the trust and efficiency of composite service. finally, the best binding scheme is discovered by an optimization method based on user specific trust metrics. In the end, experiments based on real Web services are presented to illustrate the proposed framework TWSCO can effectively guarantee the user preference trust of the composite service.

Composite services evolve for various reasons. Test case selection in the regression testing is an effective technique to ensure the correctness of modified versions meanwhile to reduce the cost of testing. However, few work has studied the test case selection problem based on the data flow testing criteria. In addition, there are three observable kinds of changes during the evolution, including Process change, Binding change and Interface change, which all bring impact to the data flow. To address these issues, a test case selection approach is proposed for regression testing of BPEL (Business Process Execution Language) composite service where all-uses criterion is satisfied and all the three change types are involved. BPEL composite service is modeled with a two-level model in which XCFG (eXtended Control Flow Graph) describes the behavior of BPEL process in the first level and WSDM (Web Service Description Model) depicts the interface information of composite service and partner services in the second level. Change impact analysis is performed to identify the affected definition-use pairs by comparing and analyzing two-level models of the baseline and evolved versions. And testing paths are generated to cover the affected definition-use pairs and select test cases based on the path condition analysis. Empirical result shows that the proposed approach is effective.

Trust is one of the most critical factors for a service requestor when selecting a service from a large pool of candidate services. However, existing web service trust models either do not consider users' preferences for different quality of service (QoS) attributes, or ignore the impact of vicious ratings on trust evaluation. To address these gaps, PHAT, a dynamic trust evaluation model with dual consideration of users' preferences and false ratings, is proposed in this paper. The model introduces an approach to automatically mine users' preferences from their requirements. The preferences are then used to determine the weight of each QoS attribute when integrating trust into multi-dimensional QoS attributes. The “local” trust on a service is derived by combining the trust on QoS attributes and the user's subjective ratings. Then, the users are divided into different groups according to their QoS preferences, and the honesty of each group is assessed by filtering out dishonest users based on a hybrid approach combining rating consistency clustering with an average method. Finally, the weight on ratings is dynamically adjusted according to the results of honesty assessment when calculating the global trustworthiness, namely, the reputation of a service. The proposed model is evaluated with real-world QoS data, and the results indicate that PHAT works well on personalized evaluation of trust, and can effectively dilute the influence of malicious ratings.

Web service is a widely used implementation technique under the paradigm of Service-Oriented Architecture (SOA). A service-based system is subjected to continuous evolution and regression testing is required to check whether new faults have been introduced. Based on the current scientific work of web service regression testing, this survey aims to identify gaps in current research and suggests some promising areas for further study. To this end, we performed a broad automatic search on publications in the selected electronic databases published from 2000 to 2013. Through our careful review and manual screening, a total of 30 papers have been selected as primary studies for answering our research questions. We presented a qualitative analysis of the findings, including stakeholders, challenges, standards, techniques, and validations employed in these primary studies. Our main results include the following: (1) Service integrator is the key stakeholder that largely impacts how regression testing is performed. (2) Challenges of cost and autonomy issues have been studied heavily. However, more emphasis should be put on the other challenges, such as test timing, dynamics, privacy, quota constraints, and concurrency issues. (3) Orchestration-based services have been largely studied, while little attention has been paid to either choreography-based services or semantic-based services. (4) An appreciable amount of web service regression testing techniques have been proposed, including 48 test case prioritization techniques, 10 test selection techniques, two test suite minimization techniques, and another collaborative technique. (5) Many regression test techniques have not been theoretically proven or experimentally analyzed, which limits their application in large-scale systems. We believe that our survey has identified gaps in current research work and reveals new insights for the future work.

The relatively new web service software paradigm involves services which are loosely coupled, highly reusable and flexible. By specifying the workflow of individual services, Web service composition enhances the ability to handle more complex business processes and provides many value-added services. In this article, we propose an extended control flow graph (XCFG) to formally model the workflow of Web service composition specified in BPEL, and corresponding techniques to verify concurrent properties, such as deadlock-free, non-conflict, and link non-redundant. XCFG can model not only the workflow of BPEL but also the synchronization control dependencies among concurrent activities. Meanwhile, each element of XCFG keeps record of related information of corresponding activity in BPEL so as to support further analysis and verification. Experimental study validates the effectiveness and efficiency of the proposed XCFG-based technique.

SOA (Service-oriented Architecture) is becoming the major architecture for building complex Web service systems. In SOA, the lifecycle of Web services consists of four stages: service publication, service discovery, service binding and service execution. Faults may occur in any stage and cause a failure of service. The reliability of services depends on not only the faults of the remote services itself, but also the faults that may occur in any SOA stage. Designing an effective and accurate reliability prediction model for Web services has become an important and necessary task. This study first proposes a staged reliability model for atomic services, which structures the reliability estimation based on the faults that may occur at each stage. Then, the reliability of composite services or service systems can be estimated based on this staged model. An experiment is conducted to study the influence of failures at each stage on the reliability of atomic services and a case study is designed to demonstrate the reliability of composite services using our staged model. In addition, the accuracy of our approach is investigated by comparing it against CBRM (component-based reliability model). Sensitivity analysis is also performed to identify critical service. Experimental results show that our staged model can obtain higher reliability prediction accuracy and is more suitable for Web services than traditional model.

BPEL(Business Process Execution Language) composite service evolves a lot in its lifetime. Regression testing must be performed to ensure the correctness of each evolved version. In this article, an approach is proposed to select test cases for regression testing based on data flow testing criterion. With XCFG(eXtended Control Flow Graph) modeling BPEL composite service, the approach improves the traditional data flow analysis to compute the def-use pairs in BPEL process, and then identifies the affected def-use pairs by comparing the def-use pairs and XCFG model in the evolved version with those in the baseline version, where related WSDL(Web Service Description Language) documents are incorporated for comparison. The data flow paths covering the affected def-use pairs are calculated for regression testing, and some of them can reuse the test cases in the baseline version, which are determined by analyzing the path condition of data flow paths between two versions. The proposed approach can detect three kinds of changes, including process change, binding change and interface change. Experimental study shows the effectiveness.

Highlights? We propose a flow graph to model BPEL-based composite service. ? XBFG path is introduced and analyzed for test case selection. ? A new classification for service modification is discussed. ? Five different versions of a running example are explored. Services are highly reusable, flexible and loosely coupled components whose changes make the evolution and maintenance of composite services more complex. The changes of composite service mainly cover three types, i.e., the processes, bindings, and interfaces. In this article, an approach is proposed to select test cases for regression testing of different versions of BPEL (business process execution language) composite service where these changes are involved. The approach identifies the changes by performing control flow analysis and comparing the paths in a new version of composite service with those in the old one using a kind of eXtensible BPEL flow graph (XBFG). Message sequence is appended to XBFG path so that XBFG can fully describe the behavior of composite service. The binding and predicate constraint information added in different XBFG elements can be used for path selection and even for test case generation. Both theoretic analysis and case study show that the proposed approach is effective.

In web service times, the techniques for composing services are based on service reuse and automatic integration. A new web service will be generated by composing some existing web services. These web services cooperate with each other to provide a new more complex function. It is necessary and very important to test the interaction behavior between any two web services during composition. In this paper, a kind of enhanced hierarchical color petri-net (or EH-CPN) is introduced to generate test cases for testing the interaction, where EH-CPN is transformed from OWL-S document, and both control flow and data flow information in EH-CPN are analyzed and used to generate an executable test sequence, and further test cases are created by combining the test sequence and test data in an XML file.

BPEL composite service inevitably evolves to meet various requirements. Most researchers only consider the verification of single versions. However, applying the original costly verification method to subsequent versions during evolution is very expensive, especially for large systems. To address this challenge, we proposed a new approach to incrementally verify the concurrent properties of the evolved version, including deadlock-free, non-conflict and link non-redundant. With XCFG, which can formally model the BPEL process, it is convenient to identify the changes between the consecutive versions of composite service by comparing their XCFGs. Then it concentrates on the changes to incrementally analyze whether violations exist for the three concurrent properties. Finally, a case study is illustrated to show the effectiveness and efficiency of the incremental method.

In this article, we paid more attention on researching how to monitor Web services for checking conformance, where an AOP-based run-time monitoring framework was proposed and explored. In the framework, WS-Policy was firstly used to express the monitoring requirement, then monitoring requirement was described as AOP monitoring logic, Active BPEL engine was extended to weave the monitoring logic and the service core execution logic dynamically, a checking algorithm was introduced to analyze whether the user's monitoring requirement was satisfied according to MREG (Monitoring Requirement Expression Graph) and EMSC (Extended Message Sequence Charts), and finally, some control and modification measures were adopted in order to rise the quality of the service composition.

Trust is one of the most critical quality factors for service requestors when they select the services from a large pool of Web services. However, existing web service trust models either do not focus on satisfying user's preferences for different quality of service (QoS) attributes, or do not pay enough attention to the impact of malicious ratings on trust evaluation. To address these gaps, a user-oriented trust model considering user's preferences and false ratings is proposed in this paper. The model introduces an approach to automatically mine user's preferences from their requirements, the preferences are used to determine the weights of each QoS attribute when integrating local trust into the multi-dimensional QoS attributes. The local trust on a service for the user is derived by combining the trust on QoS attributes and the trust on user's ratings. In this model, the users are classified into different groups according to their preferences, the honesty of each group is assessed by filtering out dishonest users using a hybrid approach which combines rating consistency clustering and an average method. To calculate the global trustworthiness of a service for the users group, the weight of ratings is dynamically adjusted according to the results of honesty assessment. The simulation results indicate that the model works well on personalized evaluation of trust, and it can effectively dilute the influence of malicious ratings.

Trust is one of the most critical factors for a service requestor when selecting the best one from a large pool of services. However, existing web service trust models either do not focus on satisfying customer's preference for different quality of service (QoS) attributes, or do not pay enough attention to the impact of malicious ratings on trust evaluation. To address these gaps, a dynamic trust evaluation model considering customer's preference and false ratings is proposed in this paper. The model introduces an approach automatically mining customer's preference from their requirements. The preference is used to determine the weights on each QoS attribute when integrating trust of the multi-dimensional QoS attributes. The local trust of a service for the customer is derived by combining trust of QoS attributes and customer's ratings. Then, the customers are divided into different groups according to their preferences, and the honesty of each group is assessed by filtering out dishonest customers based on a hybrid approach combining rating consistency clustering and average method. Finally, the weight on ratings is dynamically adjusted according to the results of honesty assessment when calculating the global trustworthiness of a service for the user group. The simulation results indicate that the model works well on personalized evaluation of trust, and it can effectively dilute the influence of malicious ratings.

As an important method for creating value-added services by composing existing services, Web service composition technology has attracted an increasing attention in recent years. Most current service composition and optimization methods utilize quality of service (QoS) attributes to decide which concrete services to invoke. However, trust which is of critical importance to service composition processes is ignored in these methods. To solve the problem, a trust-based service composition and optimization method is proposed in this paper. First, the trust of service composition is defined in terms of the trust of component service selection processes, composition processes and optimal binding plans. Second, a framework is proposed to guarantee the trust of service composition. In the framework, the trust of component service selection processes is guaranteed by filtration, and the trust of composition processes is guaranteed by interface-based service clustering methods. In order to find a trustworthy binding plan, a trust evaluation method is also included in the framework. Finally, a case study based on real Web services is presented, and the experimental results show that the framework can effectively guarantee the trust of service composition and optimization processes.

Changes to a composite service need to be well analyzed in order to ensure the trust of it. The analysis can be driven by identifying the impact caused by the changes on the trust of other component services as well as the composite service. In this paper, we propose a trust impact analysis model to analyze the impact of two kinds of evolution operations performed on a composite service: binding changes and business process changes. First, trust dependency graph is introduced to analyze the impact on the trust of component services. It not only identifies the affected component services but also quantifies the impact degree on the trust of them. Then we introduce control flow graph to evaluate the impact on the trust of the composite service. Three metrics are introduced to evaluate the impact of these evolution operations. The case study shows how these evolution operations affect the trust of other component services and the composite service which provides a foundation for the evaluation of composite service evolution.

In SOA (Service-oriented Architecture), web services consist of five steps: service publishing, service discovery, service composition, service binding and service execution. Faults may occur during every step and cause failure of service execution. Traditional architecture-based reliability models are inapplicable to web services. In this paper, a staged reliability model for web services is proposed which divides the model into multistage model based on the faults occurred at every step. This model considers more failure factors than traditional model.

Reliability has become a major quality metric for Web service. However, current reliability evaluation approaches lack a formal semantic representation and the support of incomplete or uncertain information. We propose a Web service reliability ontology (WSRO) serving as a basis to characterize the knowledge of Web service. And based on WSRO, a mapping to the probability graphical model is constructed. The Web service reliability evaluation results are obtained by the causality reasoning. Some evaluation results reveal that our approach is applicable and effective.

In this article, an approach is proposed to evaluate the reliability of Web services, where three kinds of Web services are discussed, they are atomic service without the structural information, structural activity based composite service which is composed from other services by using a structural activity mechanism, and BPEL flow process based composite service which composes all kinds of atomic services and activity based composite services using BPEL language in an orchestration style. Firstly, the reliability of atomic service is evaluated based on an extended UDDI model, then, the reliability of activity based composite services is evaluated using BPEL code structure analysis, the reliability of atomic service, and function transition probability, finally, the reliability of BPEL flow process based composite web service was evaluated by a recursive algorithm. Case study and experimental results show the significance of the approach.

Services are highly reusable, flexible and loosely coupled, which makes the evolution and the maintenance of composite services more complex. Evolution of BPEL composite service covers changes of processes, bindings and interfaces. In this paper, an approach is proposed to select and generate test cases during the evolution of BPEL composite service. The approach identifies the changes by using control-flow analysis technique and comparing the paths in new composite service version and the old one using extensible BPEL flow graph (or XBFG). Message flow is appended to the control flow so that XBFG can describe the behavior of composite service integrally. The binding and predicate constraint information added in XBFG elements can be used in path selection and test case generation. Theory analysis and case study both show that the approach is effective, and test cases coverage rate is high for the changes of processes, bindings and interfaces.

Service composition, which provides a more effective way to combine several single services into a composite service, is a kind of software reuse techniques. However, one of the most important problems is how to perform service composition correctly and effectively so as to produce high-quality source codes for describing the resulted composite service. In this paper, we propose a model-driven method to solve this problem, where UML 2.0 sequence diagrams are extended to model the composition of web services, extended statecharts are synthesized from sequence diagrams, then the statecharts are further transferred to the input language of a model checker for behavior consistency checking, and finally verified BPEL codes can be generated from improved sequence diagrams. Case studies have been performed to demonstrate the whole process and illustrate the significance of our approach.

With the loose coupling and dynamic attributes of Web Service, the implementation behavior may be different from original requirement, so it’s essential to implement the run-time monitoring. Monitoring analyzes the conformance of a Web Service to the requirements. This paper gives a novel monitoring prototype framework. It introduces WS-Policy to express the user’s monitoring requirement on the Services. Then, AOP (Aspect Oriented Programming) technology is used to extend the BPEL execution engine in order to capture run-time information of the service. Finally, monitoring information is analyzed against the EMSC (Extended Message Sequence Charts) and METG property specification of that service, reaching the predefined goal of monitoring. To evaluate our approach, we have executed a travel reservation service sample under the monitoring framework. Case study demonstrates the feasibility.

In this article, a user-oriented software reliability model was proposed to evaluate the reliability of Web services two kinds of Web services were discussed: atomic services without the structural information and the composite services consisting of atomic services. Firstly, the reliability of atomic service was evaluated based on an extended UDDI model. Then, the overall reliability of composite service was evaluated using BPEL structure chart-based model and the reliabilities of all atomic services being used. A case study is designed, implemented, and analyzed to support our model. The experimental results show the significances of the model.

Keeping composite services satisfying desired properties has been widely accepted as an important and challenging problem due to the dynamically evolving attribute of web service compositions. Runtime monitoring and dynamic verification techniques become first class activities to be performed during the execution of web service compositions. Scenario-based temporal properties depicting the complex interactions among the different services are a kind of important property which needs to be monitored at runtime. However, some complex scenario-based temporal properties cannot be easily represented by the traditional formalism such as temporal logic. In this paper, we first propose to represent the scenario-based temporal properties of web service compositions by the use of a novel notation (Property Sequence Chart). Then, we use Aspect-Oriented Programming techniques to extend the open-source BPEL engine (ActiveBPEL) and monitor its execution. Based on these assumptions, we propose a more intuitive approach to monitor the scenario-based temporal properties in web service compositions.

Due to the dynamically evolving attribute, validation of composite services must be extended from design time to run-time. Dynamical verification techniques, such as runtime monitoring, have been first class activities to be performed during the execution of composite services. For a kind of composite services, nonfunctional properties, such as timed properties, are as important as functional properties and need to be monitored at run-time. However, using traditional logic and formalism, these timed properties are not easily represented for general software engineers. In order to deal with this problem, we first extend a novel notation (Property Sequence Chart) with time constructs. Then, we give its semantics in terms of timed Buchi automata and measure its expressiveness based on recently proposed real-time specification patterns. Finally, we propose a novel framework to monitor two kinds of timed properties in composite services: the accomplished time of basic service operations and some additional timed assumptions of the composition process. Our framework provides a completely graphical front-end which can friendly help general software engineers to monitor the timed properties in composite services.

Runtime monitoring is significantly essential for web service compositions. For a kind of composite services, nonfunctional properties, such as timed properties, are as important as functional properties and need to be monitored in runtime. In this paper, we extend properly sequence chart into timed properly sequence chart and propose a new approach to monitor two kinds of timed properties in web service compositions: the accomplished time of basic service operations and some additional timed assumptions of the composition process. Our approach is more intuitive than traditional monitoring approaches.

The formal description of Web service is the basis for analyzing and verifying the Web service composition. In this article, a simple pattern-oriented mathematical model for Web service composition is introduced according to following steps: firstly, single service model is formally defined; secondly, several kinds of interaction logics between services are discussed and the composition pattern is presented, the realization of the interaction logics are given at the same time; thirdly, the definition of Web service composition model and the algorithms are presented; finally, a running example is discussed based on our model. The model can express the interactive logic relationships between messages well and it can also be used to simulate the interaction between services via message passing.

It is very difficult to construct correct component behavior models for distributed, reactive system. The concept of service makes us revisit the method of how to construct component behavior models. On the contrary, current descriptions of service are mainly based on syntax. Because service lacks of a systematic semantic description, it is hard to develop service with high quality and reliability. In this paper we combine the ideas of service and component; propose a new methodology supporting automatic synthesis and verification of component behavior model. This method uses traditional scenario-based synthesis technique to synthesize each role behavior model of service, and verifies desired properties of role by model checking, then synthesizes component behavior model by composing all roles participated in different services, and verifies liveness properties of component by compositional reasoning thus avoids searching the whole state space of component.