Fault Management For Service-Oriented Systems

Service Oriented Architectures (SOAs) enable the automatic creation of business applications from independently developed and deployed Web services. As Web services are inherently unreliable, how to deliver reliable Web services composition over unreliable Web services is a significant and challenging problem. The process requires monitoring the system\u27s behavior, determining when and why faults occur, and then applying fault prevention/recovery mechanisms to minimize the impact and/or recover from these faults. However, it is hard to apply a non-distributed management approach to SOA, since a manager needs to communicate with the different components through authentications. In SOA, a business process can terminate successfully if all services finish their work correctly through providing alternative plans in case of fault. However, the business process itself may encounter different faults because the fault may occur anywhere at any time due to SOA specifications. In this work, we propose new fault management technique (FLEX) and we identify several improvements over existing techniques. First, existing techniques rely mainly on static information while FLEX is based on dynamic information. Second, existing frameworks use a limited number of attributes; while we use all possible attributes by identify them as either required or optional. Third, FLEX reduces the comparison cost (time and space) by filtering out services at each level needed for evaluation. In general, FLEX is divided into two phases: Phase I, computes service reliability and utility, while in Phase II, runtime planning and evaluation. In Phase I, we assess the fault likelihood of the service using a combination of techniques (e.g., Hidden Marcov Model, Reputation, and Clustering). In Phase II, we build a recovery plan to execute in case of fault(s) and we calculate the overall system reliability based on the fault occurrence likelihoods assessed for all the services that are part of the current composition. FLEX is novel because it relies on key activities of the autonomic control loop (i.e., collect, analyze, decide, plan, and execute) to support dynamic management based on the changes of user requirements and QoS level. Our technique dynamically evaluates the performance of Web services based on their previous history and user requirements, assess the likelihood of fault occurrence, and uses the result to create (multiple) recovery plans. Moreover, we define a method to assess the overall system reliability by evaluating the performance of individual recovery plans, when invoked together. The Experiment results show that our technique improves the service selection quality by selecting the services with the highest score and improves the overall system performance in comparison with existing works. In the future, we plan to investigate techniques for monitoring service oriented systems and assess the online negotiation possibilities for combining different services to create high performance systems

Discovery and validation for composite services on the semantic web

urrent technology for locating and validating composite services are not sufficient due to the following reasons. • Current frameworks do not have the capacity to create complete service descriptions since they do not model all the functional aspects together (i.e. the purpose of a service, state transitions, data transformations). Those that deal with behavioural descriptions are unable to model the ordering constraints between concurrent interactions completely since they do not consider the time taken by interactions. Furthermore, there is no mechanism to assess the correctness of a functional description. • Existing semantic-based matching techniques cannot locate services that conform to global constraints. Semantic-based techniques use ontological relationships to perform mappings between the terms in service descriptions and user requests. Therefore, unlike techniques that perform either direct string matching or schema matching, semantic-based approaches can match descriptions created with different terminologies and achieve a higher recall. Global constraints relate to restrictions on values of two or more attributes of multiple constituent services. • Current techniques that generate and validate global communication models of composite services yield inaccurate results (i.e. detect phantom deadlocks or ignore actual deadlocks) since they either (i) do not support all types of interactions (i.e. only send and receive, not service and invoke) or (ii) do not consider the time taken by interactions. This thesis presents novel ideas to deal with the stated limitations. First, we propose two formalisms (WS-ALUE and WS-π-calculus) for creating functional and behavioural descriptions respectively. WS-ALUE extends the Description Logic language ALUE with some new predicates and models all the functional aspects together. WS-π-calculus extends π-calculus with Interval Time Logic (ITL) axioms. ITL axioms accurately model temporal relationships between concurrent interactions. A technique comparing a WS-π-calculus description of a service against its WS-ALUE description is introduced to detect any errors that are not equally reflected in both descriptions. We propose novel semantic-based matching techniques to locate composite services that conform to global constraints. These constraints are of two types: strictly dependent or independent. A constraint is of the former type if the values that should be assigned to all the remaining restricted attributes can be uniquely determined once a value is assigned to one. Any global constraint that is not strictly dependent is independent. A complete and correct technique that locates services that conform to strictly dependent constraints in polynomial time, is defined using a three-dimensional data cube. The proposed approach that deals with independent constraints is correct, but not complete, and is a heuristic approach. It incorporates user defined objective functions, greedy algorithms and domain rules to locate conforming services. We propose a new approach to generate global communication models (of composite services) that are free of deadlocks and synchronisation conflicts. This approach is an extension of a transitive temporal reasoning mechanism