Minimum Cost Composition Algorithm for Web Service Based on 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.

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.

To deal with Failure classification and code winding,a fault-tolerant model of web service composition based on aspect oriented programming is proposed.Firstly,fault reasons at all stage of Web services during execution are analyzed and classified,appropriate fault-tolerant strategies are presented,and web service composition model are built based on separation-of-concerns.Business function and quality of service are ensured,while function concerns and fault-tolerant concerns are separated.Finally,a case study of setup planning is presented to verify the feasibility of the method.

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

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.

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.

In this paper we describe an approach for the verification of Web service compositions defined by sets of BPEL processes. The key aspect of such a verification is the model adopted for representing the communications among the services participating in the composition. Indeed, these communications are asynchronous and buffered in the existing execution frameworks, while most verification approaches assume a synchronous communication model for efficiency reasons. In our approach, we develop a parametric model for describing Web service compositions, which allows us to capture a hierarchy of communication models, ranging from synchronous communications to asynchronous communications with complex buffer structures. Moreover, we develop a technique to associate with a Web service composition the most adequate communication model, i.e., the simplest model that is sufficient to capture all the behaviors of the composition. This way, we can provide an accurate model of a wider class of service composition scenarios, while preserving as much as possible an efficient performance in verification.

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.

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.

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

The verification of Web service compositions is mainly based on model checking techniques for temporal logics. Little attention is paid to the epistemological perspectives. In this paper, we abstract an OWL-S web service composition as a multi-agent system, propose an intermediate formal model OWL-S2FSM for modeling OWL-S process models, based on which we further develop a transformation method to convert the OWL-S language to the input language of the epistemic model checker MCTK developed by us. The proposed verification approach enables us to check not only temporal properties, but also temporal-epistemic properties of OWL-S web services. The experimental results show the validity of the proposed verification approach.

Aiming at the hot and difficult issues in Web services and service composition, this paper analyzes and studies the selection of Web services and service composition from the functional and non functional attributes of Web services, and mainly makes the following work and innovation. First of all, the functional attributes of Web services are studied, Web services on various service provision platforms are collected, and Web services are classified. Secondly, aiming at the shortcomings of existing Web service QoS attribute evaluation models, an improved method is proposed, which introduces a comprehensive evaluation mechanism of variable weight vector. Based on the constant weight comprehensive evaluation method, the state variable weight vector is established to dynamically adjust the attribute weights of various service QoS indicators, so as to improve the accuracy and objectivity of the Web service QoS attribute evaluation. Finally, in view of the defects and deficiencies of traditional algorithms in the selection of Web service composition, the particle swarm optimization algorithm with linearly decreasing inertia weight and learning factor is introduced, which better balances the self cognition and social learning ability of particles, and improves the search speed and global search ability of particles. And a large number of experiments are carried out to compare it with the traditional algorithm, which verifies the effectiveness and superiority of the improved particle swarm optimization algorithm.

Managing Service Level Agreement (SLA) for composite semantic web services is a very complex process, as it involves many complex tasks such as components discovery, provisioning, monitoring, recovery, and coordination. Indeed, managing all these tasks manually is a very cumbersome operation, nevertheless it is time consuming and prone to errors. To overcome such problems, automated SLA management for composite semantic web services is needed. This requires the SLA of the composite service to be described in a machine-understandable format such that it can be understood and processed by the automated SLA management tool. Currently, there is no SLA description language for composite semantic web services, but there exists an SLA description language for atomic web services, known as the Web Service Level Agreement (WSLA). Hence, in this paper, we aim to extend the WSLA language to describe composite semantic web services' SLAs, then we show how we can automatically generate the components' SLAs from the composite semantic web services' SLAs; adopting the CRECENT framework that we previously proposed for managing composite web services.

To deal with Web service dynamicity and changes of application constraints in open distributed environment, a coordination model for dynamic service composition is presented. Based on the separation of concerns, there are three different categories of entities in a Web service-based application: Web service, role and coordinator. The Web service is only responsible for performing pure functional service, and carrying out the task assigned by the role; the role is an abstraction for certain properties and functionalities, responsible for binding Web service according to constraints, and actively coordinating Web service to achieve coordination requirements; the coordinator is responsible for the coordination among roles by imposing coordination policies and binding constraints. The logic separation of Web services, roles, and coordinators in the model, decouples the dependencies between the coordinators and Web services. Thus, the model shields the coordinator layer from the dynamicity of Web services. Finally, a vehicle navigation application including traffic control Web services, GPS Web services and a navigator is illustrated how the model can be used to achieve the interaction adaptation by means of dynamic composition of Web service.