WS-mediator for improving dependability of service composition

Web Services and service-oriented architectures (SOAs) represent a new paradigm for building distributed computing applications. In recent years, they have started to play a critical role in numerous e-Science and e-Commerce applications. The advantages of Web Services, such as their loosely coupled architecture and standardized interoperability, make them a desirable platform, especially for developing large-scale applications such as those based on cross-organizational service composition. However, the Web Service technology is now facing many serious issues that need to be addressed, one of the most important ones being the dependability of their composition. Web Service composition relies on individual component services and computer networks, particularly the Internet. As the component services are autonomous, prior to use their dependability is unknown. In addition to that, computer networks are inherently unreliable media: from the user's perspective, network failures may undermine the dependability of Web Services. Consequently, failures of individual component services and of the network can undermine the dependability of the entire application relying on service composition. Our research is intended to contribute to achieving higher dependability of Web Service composition. We have developed a novel solution, called WS-Mediator system, implementing resilience-explicit computing and fault tolerance mechanisms to improve the dependability of Web Service composition. It consists of a number of subsystems, called Sub-Mediators, which are deployed at various geographical locations across the Internet to monitor Web Services and dynamically generate Web Service dependability metadata in order to make resilience-explicit decisions. In addition to applying the fault tolerance mechanisms that deal with various kinds of faults during the service composition, the resilience-explicit reconfiguration mechanism dynamically selects the most dependable Web Services to achieve higher service composition dependability fault tolerance. A specific instance of the WS-Mediator architecture has been developed in the Java Web Service technology. A series of experiments with real-world Web Services, in particular in the bioinformatics domain, have been carried out using the Java WS- Mediator. The results of the experiments have demonstrated the applicability of the WS-Mediator approach.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Fault injection testing method of software implemented fault tolerance mechanisms of web service systems

Testing Web Services applications and their Fault Tolerance Mechanisms (FTMs) is crucial for the development of today's applications. The performance and FTMs of composed service systems are hard to measure at design time because service instability is often caused by the nature of the network. Testing in a real internet environment is difficult to set up and control. However, the adequacy of FTMs and the performance of Web Service applications can be tested efficiently by injecting faults and observing how the target system performs under faulty conditions. This thesis investigates what is involved in testing the software-implemented fault tolerance mechanisms of Web Service systems through fault injection. We have developed a fault injection toolkit that emulates a WAN within a LAN environment between composed service components and offers full control over the emulated environments, in addition to the ability to inject communication and specific software faults. The tool also generates background workloads on the tested system for producing more realistic results. The testing method requires that the target system be constructed as a collection of Web Services applications interacting via messages. This enables the insertion of faults into the target system to emulate the incorrect behaviour of faulty conditions by injecting communication faults and manipulating messages. This approach allows the injection of faults while not requiring any significant changes to the target system. This testing method injects two classes of faults, manly communication and interface faults due to their big impact on Web service system dependability. The method differs from the previous work not only by injecting communication faults based on a Wide Area Network emulator, but also in its ability to inject a combination of communication and interface faults, which could cause what are called Byzantine faults (Arbitrary faults) at the application level. The proposed fault injection method has been applied to test a Web Service system deploying what is called a WS-Mediator for improving the system reliability. The WS-Mediator claims to offer comprehensive off-the-shelf fault tolerance mechanisms to cope with various kinds of typical Web Service application scenarios. We chose to use the N-version programming mechanism offered by the WS-Mediator, which has been tested through out tool. The testing demonstrated the usefulness of the method and its capacity to test the target system under different circumstances and faulty conditions.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Resilience-Building Technologies: State of Knowledge -- ReSIST NoE Deliverable D12

This document is the first product of work package WP2, "Resilience-building and -scaling technologies", in the programme of jointly executed research (JER) of the ReSIST Network of Excellenc