Analyzing Service Composition Patterns in BPEL

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.

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 composition involves the combination of a number of existing web services to create a value-added one. WS-BPEL is a promising language which describes Web service composition in form of business processes. However, WS-BPEL is an XML-based language and may suffer from ambiguities or some erroneous properties. The analysis and verification of business processes specified in WS-BPEL by a formal method has been a hot topic in the research community lately. In this paper, we propose a method to model and analyze WS-BPEL business processes based on ServiceNet, a special class of Petri nets. Unlike most of the existing work which analyze only control flow properties of WS-BPEL business processes but neglect data flow properties, our method models and analyzes both control properties and data properties of WS-BPEL business processes. We present the transformation rules of WS-BPEL business processes into ServiceNet and enrich the reduction rules of ServiceNet by applying them in some practical projects. Then the throughness of a business processes can be verified by reducing its ServiceNet representation based on some reduction rules. Moreover, we define some data-aspect properties of WS-BPEL business processes and give the corresponding checking 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.

Recently, the advent of Web services gets rid of the troubles in cooperating with other systems regardless of their underlying platforms. Web services can be composed dynamically on demand and possibly produce value-added services which are mesmerizing enterprises. For dependable execution of the composite services, many failure handling and recovery schemes have been proposed. However, those schemes lack in supporting specific handling of failures as an individual user desires.In this paper, we propose a service composition framework for user-specified failure handling in web services orchestration. In this framework, an instance of executable business process is dynamically generated from common business logic with failure handling specific to each user. We also design an XML expression of a user's failure acceptance specification, and an algorithm for automatically generating an executable business process embedding user-specified failure handling, with architecture of the composite service provider for applying our proposed framework. The comparison of properties between previous works and the proposed one in terms of failure handling is provided as well.

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.

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.

Web Service has become a newly distributed computing paradigm. Modeling and analyzing the workflow of composite web services is the most important task in the process of developing service oriented software. BPEL is the industry standard used for combining a set of web services to define a new composite web service. A Petri net model- WS_Net is defined which suitable for describing the business processes of composite web services. Then, a method used for translating a BPEL process to WS_Net is presented. The reliable data of a composite web services is collected by extending UDDI model. WS_RPN which captures the reliability aspect of the web services composition and can be used for analyzing the reliability of BPEL processed through the execution paths is defined based on WS_Net. Finally an example is used to illustrate the method.

The Business Process Execution Language (BPEL) has become the standard in Web service composition, so that been adopted by industries to create mission critical services. The business process reliability especially business process consistency when some services failed is critical to composite services especially involving various organizations. However, it is difficult to conduct business process reliability testing for composite services due to complex business process in service composition, remote deployed services and long time testing duration. Little research is done to test fault tolerance capabilities of composite services only from low level. This paper proposes a technique on how to test the reliability of composite service defined in BPEL from the view of business semantics with little cost using fault injection. We present an approach for reliability testing of web services by using service stubs with semantic faults instead of real services which can be placed at service provider side or service consumer side. Dislike existing studies, we focus on how to find the reliability problems associating with business process - called semantics as the problems are not pure coding error but faults related to business process. In addition, the behavior of composite services in BPEL is analyzed when there are faults in orchestrated services invoked. Finally, a case study is given to show the whole process of reliability testing for composite web service.

Modelling and performance analysis is one of the most important issues in business processes. Built on top of web protocols and XML language, web services are emerging as a high level framework for business-to-business relationships. UML can be used to model web services interactions and reengineered diagrams using Petri nets like semantics instead of state machines. Unfortunately, the standard has failed to define formal semantics. To address this issue, this paper provides a mapping from activities to Petri net models. Formalisations basing on UML and Petri nets of control-flow patterns for service composition are addressed. We propose a high-level class of Petri nets for describing the behaviour of scenarios of web services composition. Developed models support the strong dynamic and temporal aspects of these scenarios. Translation rules from flow patterns into Petri net models are provided. Finally an illustrative example is given to show the applicability of the proposed approach.

Web services technology is emerging as a promising approach of integration and interaction for applications within and across organizational boundaries. But it is difficult to meet the practical requirements if only with the individual Web services. As a result, federating existing single Web services into composite Web services is not only necessary but also indispensable. This paper proposes a dynamic and semantic composition approach for Web services. In this approach, Web services are modeled with some rules whose heads and bodied are related with a semantic ontology used for eliminating the semantic conflicts in composition. Moreover, a nonbacktrace backward chaining algorithm is addressed to compose the existing Web services in a more efficient and automatic way. Given the inputs and expected outputs, the approach will automatically and dynamically generate a composition plan and convert it into BPEL4WS that can be executed and returns the results. The whole composition process can be done automatically and dynamically

As Web services become widespread, many complex applications require service composition to cope with high scalability and heterogeneity. Centralized Web service composition approaches are not sufficient as they always limit the scalability and stability of the systems. How to efficiently compose and adapt Web services under decentralized environments has become a critical issue, and important research question in Web service composition. In this paper, a stigmergic-based approach is proposed to model dynamic interactions among Web services, and handle some issues in service composition and adaptation. In the proposed approach, Web services and resources are considered as multiple agents. Stigmergic-based self-organization among agents are adopted to evolve and adapt Web service compositions. Experimental results indicate that by using this approach, service composition can be efficiently achieved, despite dealing with incomplete information and dynamic factors in decentralized environments.

: Web Services is an emerging paradigm in which very loosely coupled software components are published, located, and invoked on the Web as parts of distributed applications. Web Services provide a new way of distributed computing where the interoperability between diverse applications is achieved through platform and language independent interfaces. The main focus of Web Services is the ability to easily combine existing components to create compositions that provide novel functionality that was not directly available from the existing services. Web Services composition is useful for a wide range of audience: ordinary users doing everyday tasks on the Web, commercial organizations involved in e-business applications, and researchers doing intense scientific computation over distributed networks. Automated composition of Web Services requires fairly rich machine-understandable descriptions of services that can be shared between heterogeneous agents. Given appropriate descriptions, AI planning techniques can be employed to automate the composition of Web Services described this way. The purpose of this research is to show that AI planning techniques can be extended to automatically generate useful and purposeful compositions of Web Services under incomplete information. We have worked on how Web Ontology Language (WOL) can be used to describe Web Services. We have also studied how planning techniques can be used for automated composition of Web Services. In both systems, reasoning with Web Ontologies has been used to facilitate the composition task. Our goal is to investigate how these approaches can be combined with each other and can be extended to efficiently address the issues related to the nature of the Web.

E-Government services are increasingly being deployed using service-based architectures. Individual web services, developed from legacy and modern firmware, are composed to achieve e-service delivery. Current web service composition approaches range from practical languages aspiring to become standards (like BPEL, WS-CDL, OWL-S and WSMO) to theoretical models (like automata, Petri nets and process algebras). In this work, current approaches were studied and a comparison of their features and weaknesses was carried out. It was observed that current composition mechanisms are static and not agile enough to cater for functional change in business needs. This paper proposes a new web service composition and messaging mechanism for electronic government services in which composition of web services is done dynamically to provide for more agility in government e-services. The proposed composition mechanism works on a software architecture which enables application software integration. This architecture has been developed to deploy end-to-end e-services to G2B, G2C and G2G users starting from legacy government software applications. Using the proposed approach, integrating back-end e-Government applications to deliver end-to-end e-services can be agile, simpler and faster. The main contribution of this paper is the novel dynamic web service composition mechanism.

The automated composition of Web services is one of the most promising ideas and at the same time one of the most challenging research area for the taking off of service-oriented applications. It is widely recognised that one of the key elements for the automated composition of Web services is semantics, i.e. unambiguous descriptions of Web services capabilities and processes. However Web services described at capability level need a formal context to perform the automated composition of Web services. In this paper a TLB architecture (three levels based architecture) is presented to perform Web service composition. Moreover we introduce the composition process as a matchmaking of domains and solve the latter problem according to a formal model, i.e. the xCLM (eXtended causal link matrix) and a knowledge base of the domain