A Model-Driven Engineering Approach for the Formal Verification of Composite Web Services

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.

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.

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.

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.

The main method of model checking based on LTL is constructing a Büchi automata by system model and a Büchi automata equaling with the LTL denied form, and then checking the automata's acceptive language is empty or not. The idea of verifying Web Services Composition is modeling Web Services Composition by Colored Petri Net, and then using the modeling checking technique to verifying the model. It can find the fault occurring in the process of composing Web Services efficiently. Finally, an example of online shopping is used to explain the idea's correctness.

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 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.

We propose an efficient method to detect conflicts, which may occur during the execution time of composite web services, based on model checking. The proposed method does not only check whether a composite service satisfies the correctness claims specified by a service developer, but it also detects any possible conflicts from the control and data flow of a composite service at the time of service development. The proposed method divides correctness claims into four types depending on their application time: pre/post-condition, policy, and assumption. Specifically, composite services and correctness claims are modelled by OWL-S and SWRL, respectively. The proposed method automatically converts the control and data flow of an OWLS composite service and the correctness claims into Promela code and LTL formulas, which are given as the input of a SPIN model checker. Experimental results under real-world scenarios show that the proposed method detects conflicts in composite web services effectively.

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.

A High-level Petri Net Based Approach for Modeling and Composition of Web Services

With the development of Internet and Web service technology, Web service composition has been an effective way to construct software applications; service selection is the crucial element in the composition process. However, the existing selection methods mostly generate static plans since they neglect the inherent stochastic and dynamic nature of Web services. As a result, Web service composition often inevitably terminates with failure. An indeterminacy-aware service selection algorithmbased on an improved Markov decision process (IMDP) has been designed for reliable service composition, but it suffers from higher computation complexity. Therefore, an efficient method is proposed, which can reduce the computation cost by converting the service selection problem based on IMDP into solving a nonhomogeneous linear equation set. Experimental results demonstrate the success rate of service composition has been improved greatly, whilst also reducing computation cost.

The composition of Web services is an interesting option for the creation of complex applications with a wide range of features. The inherent scalability of the Internet leads to a potentially large number of services that meet a particular feature. Moreover, these services are associated with different quality indicators, sometimes conflicting. Hence, it is evident the plurality of solutions for the same problem. Considering this fact, in this work, the composition of Web services is treated as a many objective optimization problem, and multiobjective evolutionary algorithms are used to solve it. An empirical evaluation is done and the results of different preference relation techniques are compared in different composite Web services scenarios. The results show the importance of applying many-objectives techniques to problems with more than three objectives.

A web service is a software system that supports interoperable machine to machine interaction over the network. It can be any kind of service provided on the web that can exchange data between applications. In simple terms, it is any program that is callable by another program across the web using standard protocols. Web services are special because they are independent of the platform, programming language, and model design. In current web applications, more businesses are gradually publishing their business as services over the web. This growing number of web services available within an organization and on the Web raises a new and challenging search problem: locating desired web services. Searching for web services with conventional web search engines is insufficient in this context. In this paper, a latent semantic web service discovery and composition framework, addressing both discovery and composition of web services, is introduced. The framework provides a graphical visualization interface that can facilitate users in finding the desired web service beyond the general keyword search and provide composition of complex services if the service does not exist. A novel approach based on an information retrieval technique known as latent semantic analysis is applied to a large web service descriptions data set collection. By using co-occurrence patterns across the entire data collection, and then using those patterns to infer semantic relationships between documents, relevant results in a ranked order can be retrieved. Moreover, a back to front algorithm is applied to the composition search interface in order to compose complex web services in full or partial terms from pre-existing web services when the requested service does not exist. An experimental study conducted on a collection of 2525 publicity available web service shows improved performance to the technique applied in obtaining much better search results.

An efficient composition of Web services with active network support

The automatic composition of Web services requires the existing services to be encoded in a semantic form, such as ontology. If Web services are represented with ontology, we can automatic compose Web services by means of their semantics. Ontology modeling is divided into two steps: input/output parameters modeling and Web services modeling. First, we collect Web services' input/output parameters, represent them with classes in ontology, and transform Web services to properties in ontology, define relations between classes and properties. Then we judge Web services' relations based on relations between properties transformed from these Web services and estimate whether these Web services can be composed.