Verifying Web Services Composition based on LTL and colored Petri Net

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.

We propose in this paper a model-driven approach for specifying and verifying Web services composition. In particular, we present how the process engineering and reengineering allows us to check the consistency of Web services composition. To achieve this goal, we based on the Architecture Description Language (ADL) ACME. This ADL is coupled to Armani, a formal language based on first order predicates. Using MDE tools such as ATL, Xtext, Xpand and Check, we have developed a tool WSC2ACME taking as input a textual WSDL specification and outputting the corresponding ACME code. Then, we propose the re-engineering of the process to be able to use it properly, and to ensure the proper functioning of the Web services composition. Our approach aims at improving the existing proposals taking a step forward in simplifying and improving the reliability of service composition.

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.

Verification for interaction protocol of Web services is crucial to both implementation and composition of Web services. The verification process can prove important and desirable properties of the control flow and data flow of Web services. Model checking is a promising technique for verification and validation of software systems. In this paper, we present a model checking framework to specifying and verifying Web service flow based on annotated OWL-S. By using annotation layers, an OWL-S process model can be extended with constraints (like time properties) information. An underlying OWL-S model and one or more constraint annotation layers compose a complete specification of a Web process imposed specific constraints. By transforming the annotated OWL-S model to a TCPN (time constraints Petri net) model, Web service flow can be analyzed and verified. The method allows us to add conveniently constraints information to a Web process model, and state whether a process satisfies given properties without actual execution based on its specification.

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.

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.

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

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.

The increasing popularity of Web services for application integration has strengthened the need for automated Web service composition and joint execution. A lot of attention has been paid recently towards techniques for creating a composite Web service from individual Web services based on user requirements, and driven by a variety of criteria. However, the major lacuna so far in Web service composition is the lack of a holistic requirements-driven approach for modeling the Web service execution lifecycle. In this paper we present such an approach based on our earlier work on context-driven Web service modeling. In particular, we separate requirements into two parts - functional and extrafunctional requirements (FRs and EFRs, respectively). We express FRs as commitments made by individual Web ser-vices towards the composite Web service, and EFRs as rules that constrain the behavior of the individual Web services while they execute against their FRs. We also present a conceptual model that can be used for tracking requirements during Web service execution.

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.

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

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.

Web services composition is a process of creating a new web service from a set of available web services. Semi-dynamic web services composition in Service Oriented Architecture (SOA) consists of designing composition plan by service provider, and automation of web service discovery and selection at runtime. This research paper describes redundant-free web services composition in order to reduce execution time and overall cost of the composition process and also improve efficiency of the composition method. To fulfill the needs, this paper uses a linked list data structure called Composition List (CL) to select the ideal services. In addition, a hash table called Available Output Parameters (AOP) is used to find redundant web services and reject them from web services composition process.

Based on business processes, composite Web services combine the offerings of two or more Web services to achieve the desired business goals. Several candidate standards have been proposed, providing a foundation for composite Web service specifications. However, at a higher level, there is no framework that supports composite Web service construction and automation. We propose a framework that facilitates the visual design, validation and automation of composite Web services. The framework is based mainly on Web service composition graph (WSCG), the underlying formalism for composite Web services. Using graph grammar and graph transformation defined on WSCG, the static topological structure of a composite Web service can be described in an intuitive way and the automation of the constructed composite Web services is also facilitated with a sound formal semantic basis. We also outline the design and implementation of a prototype for the proposed framework.