For a system of distributed processes, correctness can be ensured by (statically) checking whether their composition satisfies properties of interest. However, Web services are distributed processes that dynamically discover properties of other Web services. Since the overall system may not be available statically and since each business process is supposed to be relatively simple, we propose to use runtime monitoring of conversations between partners as a means of checking behavioral correctness of the entire Web service system. Specifically, we identify a subset of UML 2.0 Sequence Diagrams as a property specification language and show that it is sufficiently expressive for capturing safety and liveness properties. By transforming these diagrams to automata, we enable conformance checking of finite execution traces against the specification. We show how our language can be used to specify the Specification Property System (SPS) [1]. We describe an implementation of our approach as part of an industrial system. Finally, we discuss our experience of specifying and monitoring a number of properties from three existing applications.

Regression testing assures the quality of modified service-oriented business applications against unintended changes. However, a typical regression test suite is large in size. Earlier execution of those test cases that may detect failures is attractive. Many existing prioritization techniques order test cases according to their respective coverage of program statements in a previous version of the application. On the other hand, industrial service-oriented business applications are typically written in orchestration languages such as WS-BPEL and integrated with workflow steps and web services via XPath and WSDL. Faults in these artifacts may cause the application to extract wrong data from messages, leading to failures in service compositions. Surprisingly, current regression testing research hardly considers these artifacts. We propose a multilevel coverage model to capture the business process, XPath, and WSDL from the perspective of regression testing. We develop a family of test case prioritization techniques atop the model. Empirical results show that our techniques can achieve significantly higher rates of fault detection than existing techniques.

For providers of composite services preventing cases of SLA violations is crucial. Previous work has established runtime adaptation of compositions as a promising tool to achieve SLA conformance. However, in order to get a realistic and complete view of the decision process of service providers, the costs of adaptation need to be taken into account. In this paper we formalize the problem of finding the optimal set of adaptations, which minimizes the total costs arising from SLA violations and the adaptations to prevent them. We present possible algorithms to solve this complex optimization problem, and detail an end-to-end system based on our earlier work on the PREvent (prediction and prevention based on event monitoring) framework, which clearly indicates the usefulness of our model. We discuss experimental results that show how the application of our approach leads to reduced costs for the service provider, and explain the circumstances in which different algorithms lead to more or less satisfactory results.

Abstract. One of the main benefits of service-based systems is the loose coupling of components, which increases flexibility during the selection of internal and external business partners. However, currently this flexibility is severely limited by the fact that components have to provide not only the same functionality, but do so via virtually the same interface. Invocation-level mediation may be used to overcome this issue – by using mediation interface differences can be resolved transparently at runtime. In this paper we present the general concepts of invocation-level mediation, and show how these ideas are integrated into our dynamic service invocation framework Daios. To demonstrate the flexibility of our mediation framework we present two fundamentally different mediation strategies, one based on structural similarity and one based on semantically annotated WSDL. 1

The current state of the art concerning the problem of service substitution raises the following issue: the complexity of the substitution process scales up with the number of available services that may serve as candidate substitutes for a target service. To deal with this issue, we propose a framework that is based on two substitution relations and corresponding theorems. The proposed relations and theorems allow organizing available services into groups. Then, the complexity of retrieving candidate substitute services for the target service and generating corresponding adapters scales up with the number of available groups, instead of scaling up with the number of available services. 1.

Abstract—In this paper, we address the problem of selfadaptation in internet-scale service-oriented systems. Services need to adapt by select the best neighboring services solely based on local, limited information. In such complex systems, the global significance of the various selection parameters dynamically changes. We introduce a novel metric measuring the distribution and potential impact of service properties affecting such selection parameters. We further present an formalism identifying the most significant properties based on aggregated service interaction data. We ultimately provide a ranking algorithm exploiting these dynamic interaction characteristics. Experimental evaluation demonstrates scalability and adaptiveness of our approach. I.

Service-based systems that are dynamically composed at run time to provide complex, adaptive functionality are currently one of the main development paradigms in software engineering. However, the Quality of Service (QoS) delivered by these systems remains an important concern, and needs to be managed in an equally adaptive and predictable way. To address this need, we introduce a novel, tool-supported framework for the development of adaptive service-based systems called QoSMOS (QoS Management and Optimisation of Service-based systems). QoSMOS can be used to develop service-based systems that achieve their QoS requirements through dynamically adapting to changes in the system state, environment and workload. QoSMOS service-based systems translate high-level QoS requirements specified by their administrators into probabilistic temporal logic formulae, which are then formally and automatically analysed to identify and enforce optimal system configurations. The QoSMOS self-adaptation mechanism can handle reliability- and performance-related QoS requirements, and can be integrated into newly developed solutions or legacy systems. The effectiveness and scalability of the approach are validated using simulations and a set of experiments based on an implementation of an adaptive service-based system for remote medical assistance.

Abstract. The emergence of large-scale online collaboration requires current information systems to be apprehended as service ensembles comprising human and software service entities. The software services in such systems cannot adapt to user needs based on autonomous principles alone. Instead system requirements need to reflect global interaction characteristics that arise from the overall collaborative effort. Interaction monitoring and analysis, therefore, must become a central aspect of system self-adaptation. We propose to dynamically evaluate and update system requirements based on interaction characteristics. Subsequent reconfiguration and replacement of services enables the ensemble to mature in parallel with the evolution of its user community. We evaluate our approach in a case study focusing on adaptive storage services. 1

Abstract. In this paper we show how the application of the aspectoriented programming paradigm to runtime adaptation of service compositions can be used to prevent SLA violations. Adaptations are triggered by predicted violations, and are implemented as substitutions of fragments in the service composition. Fragments are full-fledged standalone compositions, and are linked into the original composition via special activities, which we refer to as virtual activities. Before substitution we evaluate fragments with respect to their expected impact on the performance of the composition, and choose those fragments which are best suited to prevent a predicted violation. We show how our approach can be implemented using Windows Workflow Foundation technology, and discuss our work based on an illustrative case study. 1

Abstract. Service-oriented computing (SOC) increases flexibility of IT systems and helps enterprises to meet their changing needs. Different methods address changing requirements in service-oriented environment. Many solutions exist to address variability, however, each solution is tailored to a specific problem, e.g. at one specific layer in SOC. We survey variability mechanisms from literature and summarize solutions, consequences, and possible combinations in a pattern catalogue. Based on the pattern catalogue, we compare different variability patterns and their combinations. Our catalogue helps to choose an appropriate technique for the variability problem at hand and illustrates its consequences in SOC. 1