Fault-tolerant model of web service composition based on Aspect Oriented Programming

To deal with the problems such as Web Services selection algorithm, availability of Web Services composition and QoS(Quality of Service) guarantee, presents a model for Web Services composition based on QoS and providers' benefit. In this model, the traditional UDDI is expanded to describe the QoS attributes of Web Services. A Service Proxy role is added into this model. All Web Services compositions requested by service consumers are fond, bound and invoked by the Service Proxy role. In order to maximize services providers' benefit, presents a Service Request Queue Scheduling algorithm in the Service Proxy role. This model meets the QOS requirements of service consumers, guarantees the availability of Web Services composition and maximizes service providers' benefit. Experimental results confirm the efforts of this model.

Web service development and composition are mainly realized using programming languages. The high demand of productivity in the development of composite Web service requires different approaches. Conceptual modeling could be a solution. In this work we present an approach to conceptual modeling of Web service composition. Considering that a composite Web service is a way of implementing functionality reuse, we propose to use aggregation and specialization relationships (at conceptual level) with a precise semantics as mechanisms to allow the composition characterization. These conceptual models could be included in other methods (as Web engineering methods) or models in order to capture the integration requirements needed to define collaborative applications.

Web service composition is a hot and active research area in service oriented architecture (SOA). With highly developing of Web service, users pay more and more attention to quality of service (QoS). In order to obtain high comprehensive quality composite services, an optimizing method was presented in this paper. Firstly, build representative QoS properties quantitative models and QoS aggregation models, then proposed the mathematical model of Web service composition optimizing problem. Secondly, presented an improved artificial bee colony algorithm (I-ABC) and applied to solving Web service composition optimizing problem, I-ABC performance was enhanced by importing taboo strategy and chaos. Finally, some simulation experiments are given, and the results proved I-ABC has perfect performance in Web service composition optimizing than ABC

Modeling and Verification of Response Time of QoS-aware Web Service Composition by Timed CSP

As the capability of an individual Web service is limited, it's necessary to create new functionalities with existing Web services. Web services composition is the ability to create a new value-added service by incorporating some existing Web services together. An important challenge for Web services composition is how to ensure the correctness and reliability of the WS-BPEL (Web services business process execution language) process and the composition. A graphical and formal modeling tool suitable for solving this problem is CPN (Colored Petri net), which provides formal semantics and a number of analysis techniques for modeling and verifying web services composition. This paper proposes a CPN-based model for web services composition, describes how to translate WS-BPEL to CPN model, and discusses the analysis and verification of services composition. The model enables efficient composition of Web services and validates the correctness of composition by formal verification.

Traditional formal method has been solved the problems of functional modeling and verification of Web service composition, but it could not effectively analyze and calculate the costs of the service composition. A minimum cost composition algorithm based on process algebra CSP is proposed. The algorithm first translates the XML format Web service composition description to CSP format formal description. According to the trace model of the CSP, the executive paths for the proper composition schemes can be found. Finally, the total cost of the composition schemes can be solved out according to the cost of the single event in the web services' interfaces. A case study is presented that shows the algorithm can effectively calculate the total costs of the composition schemes, and the optimal scheme can be pick out refer to the results.

The paper summarizes current technologies of dynamic web service composition. Then, based on the existing technologies, we raise a new solution for dynamic web service composition. We make use of the knowledge of domain ontology. On the one hand, the user’s requirement was broken down into a series of abstract web services, according to the logic of business processes. On the other hand, through establishing the web service index storehouse, we gather the existing atomic services and composite services in domain ontology. By semantic matching between the abstract services and the atomic services or the composite services, the executable web services composition could be obtained. Finally, an application example of the solution is showed.

To enforce reliability of composite Web Services at run-time, this paper proposes a transaction management model based on Compensation Planning Graph for Web Service composition. First, a web service composition model with transactional properties is introduced. Second, in order to handle transaction when exceptions are occurred, compensation dependency relationships and Compensation Planning Graph is introduced, and an algorithm of automatic generation of compensation dependency relationships and transaction handling based on CPG is proposed. Finally, evaluation methods of QoS of web services and user satisfaction of transaction handling are given. During the execution of composite web services, this approach can guarantee compensation achieving through forward- or backward-compensation. In addition, in this model, a novel concept named Transfer Service is proposed to solve the problem that there are no compensation services or unsuccessful retriable services after many retry times. This model and method can improve self-adjustability and stability of composite services in the course of deployment and execution. Simulations prove that this approach can efficiently guarantee the reliability of composite services at run-time.

In the environment of Internet of things, devices are encapsulated as web services and device operations are encapsulated as web service methods. These web services are stateful because devices can't be controlled by more than one client at the same time. Traditional web service composition methods are lack of considering state of the web services and have great challenge under Internet of things. In this paper, a three-layer model for modeling stateful web services composition based on extended Petri net is proposed. It includes web services layer, ws-resource layer and process layer. A method of a web service is abstracted as a ws-resource. There are two types of ws-resources: exclusive resources can be invoked serially, non-exclusive resources can be invoked simultaneously. In this model, a web service is associated with one or more ws-resources, a web service can be invoked only when all needed ws-resources are available. Finally an example is demonstrated to illustrate how this model works.

This paper proposes the concept of business events as the cornerstone to web service description and coordination. First, a web service architecture is introduced as the result of an event based analysis & design phase. Then, it is advocated how the event concept can be used for semantically rich web service description. A distinction is made between two web service interfaces: a non-transactional query interface and a transactional event notification interface. Furthermore, a web service composition model is proposed, based on event broadcasting and event preconditions, instead of traditional one-to-one method invocations. The composition model is presented in a static variant and in a version with dynamic subscription. Throughout the paper, it is shown how the event based approach fits entirely within the current standard SOAP/WSDL/UDDI web services stack.KeywordsRemote ServiceQuery InterfaceMethod InvocationInput ServiceBusiness EventThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Web service composition (WSC) is the task of combining a chain of connected single services together to create a more complex and value-added composite service. Quality of service (QoS) has been mostly applied to represent nonfunctional properties of web services and differentiate those with the same functionality. Many research has been done on QoS-aware service composition, as it significantly affects the quality of a composite service. However, existing methods are restricted to predefined workflows, which can incur a couple of limitations, including the lack of guarantee for the optimality on overall QoS and for the completeness of finding a composite service solution. In this paper, instead of predefining a workflow model for service composition, we propose a novel planning-based approach that can automatically convert a QoS-aware composition task to a planning problem with temporal and numerical features. Furthermore, we use state-of-the-art planners, including an existing one and a self-developed one, to handle complex temporal planning problems with logical reasoning and numerical optimization. Our approach can find a composite service graph with the optimal overall QoS value while satisfying multiple global QoS constraints. We implement a prototype system and conduct extensive experiments on large web service repositories. The experimental results show that our proposed approach largely outperforms existing ones in terms of solution quality and is efficient enough for practical deployment.

Semantic web technology can be applied to a wide range of application domains. Educational-offer selection is an area of the education domain, which can benefit greatly from the application of semantic web technology. The paper explores the educational-offer selection problem as an application of semantic web technology. It specifically deals with the problem of higher education admission. A semantic web-based model for educational-offer selection is presented. Further, Semantic Web Service (SWS) selection and composition models are shown to be applicable to the problem of educational-offer selection. A prototype system, implementing semantic web-based educational-offer selection, is presented.

In the Web Service Composition (WSC) domain, Web Services (WSs) execute in a highly dynamic environment, as a result, the Quality of Service (QoS) of a WS is constantly evolving, and this requires tracking of the global optimization overtime to satisfy the users’ requirements. In order to make a WSC adapt to such QoS changes of WSs, we propose a self-healing model for WSC. Self-healing is the automatic discovery, and healing of the failure of a composite WS by itself due to QoS changes without interruption in the WSC and any human intervention. To the best of our knowledge, almost all the existing self-healing models in this domain substitute the faulty WS with an equivalent one without paying attention to the WS selection processes to achieve global optimization. They focus only on the WS substitution strategy. In this paper, we propose a self-healing model where we use our hybrid approach to find the optimal WSC by using Parallel Genetic Algorithm based on Q-learning, which we integrate with K-means clustering (PGAQK). The components of this model are organized according to IBM’s Monitor, Analyse, Plan, Execute, and Knowledge (MAPE-K) reference model. The PGAQK approach considers as a module in the Execute component. WS substitution strategy has also been applied in this model that substitutes the faulty WS with another equivalent one from a list of candidate WSs by using the K-means clustering technique. K-means clustering is used to prune the WSs in the search space to find the best WSs for the environment changes. We implemented this model over the NET Framework using C# programming language. A series of comparable experiments showed that the proposed model outperforms improved GA to achieve global optimization. Our proposed model also can dynamically substitute the faulty WSs with other equivalent ones in a time-efficient manner

This paper presents a formal specification of the Assurance Point (AP) web service composition model. The AP model provides a flexible way of checking constraints and responding to execution errors in service composition. An AP is a combined logical and physical checkpoint, providing an execution milestone that stores critical data and interacts with integration rules (IRs) to alter program flow and to invoke different forms of recovery depending on the execution status. In this paper, the execution and recovery semantics of assurance points have been fully defined in the context of if-else, parallel, and loop control structures. The activities and complex control structures of the AP model have been formalized and tested in the Yet Another Workflow Language (YAWL) engine. By doing so, the correctness of the execution and recovery semantics in the AP model has been verified, demonstrating that YAWL nets of the AP model satisfy the soundness property. Different from existing web service composition models, the AP model presented by this research provides multiple levels of protection against service execution failure with a combination of forward and backward recovery techniques.

The article describes a method for developing and modelling composite web-services. Web-service composition is used to derive new functionality from the interaction of existing web-services. Composite web-services are built in several stages: specifications (determining the type of service); development of the structure of the service based on the algebra of services; service composition modelling; selecting a service variant and generating a service. The main elements of the proposed approach are the algebra of services and web-services interaction models (basic and composite). The above approach formally presents the consideration of the main aspects in solving problems related to the construction of effective composite web-services and the selection of mathematical models, namely: description of web-services, determining the structure of web-services, taking into account the dynamics of information changes, taking into account the main uncertainties in building the structure web-services. Based on the approach, a method for constructing composite web-services has been developed. The method is based on an algebraic description of a web-service based on a specialized algebra of services. The method consists of the following steps: description of the task of developing a web-service; development of the structure of a web service based on the algebra of services; formal description of the structure and clarification of service operations; building models of functioning and interaction of service components; building simulation models of the composite service; defining the final structure of the composite service; web-service implementation. The main tool for describing composite services is the algebra of services, and the model building tool is colouredPetri nets implemented using СPN Tools. As an example of the application of the developed method, the construction of a pharmaceutical service is described, in which the modellingof the interaction of web-services based on Petri nets is used. The process of building a composite model of a web-service is considered. The process begins with building a pharmaceutical web-service model structure based on the service algebra. Based on the service algebra, operators were developed to implement composite services. The structure of the model is developed, which is presented in the form of a formal description. The process of building pharmaceutical service models in the СPN Tools environment is described in detail.