On context-independent and context-aware cloud services substitutability verification

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.

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.

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.

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.

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.

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

: 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.

THE Internet, along with its related technologies, has created an interconnected world in which information flows easily and tasks are processed collaboratively. To make service-oriented applications more robust, Web services must be examined from a transactional perspective. By transactional, we mean first defining the actions that guide the execution of Web services when failures arise and then the states that permit claiming the success of this execution following the handling of these failures. A variety of transactional models are reported in the database community. Some of these models can be leveraged and enhanced in response to Web services characteristics while others are not suitable for Web services due to the dynamic nature of Web services, the long-running execution scenarios that Web services take part in, and the successful execution of Web services despite other peers’ failure. Today’s service-oriented applications require advanced transactional models that guarantee integrity and continuity of business processes despite the dynamic nature of the features of the environments hosting the execution of these applications. This special section sheds light on the latest advances in the fields of Web services and transactional models in order to better address advanced research on and experience with transactional Web services. Four papers out of 19 submissions were selected for inclusion in this special section. Each submission was subject to a double-review process by at least three peer reviewers. In the first paper, entitled “Event-Based Design and Runtime Verification of Composite Service Transactional Behavior,” Gaaloul et al. propose an event-driven approach to validate the transactional behavior of Web services taking part in compositions. A composition life cycle consists of four phases, namely, design, execution, monitoring, and reengineering. The verification of this behavior throughout this life cycle is done either at design time to validate recovery mechanisms’ consistency or after runtime to detect execution deviations and repair design errors, and, therefore, formally ensure the execution reliability of Web services. In addition, this verification is based on the Event Calculus formalism, which offers a sound definition for this reliability. In the second paper, entitled “FACTS: A Framework for Fault-Tolerant Composition of Transactional Web Services,” Liu et al. note that delivering reliable compositions over unreliable Web services is challenging. To address this challenge, Liu et al. identify a set of high-level exception handling strategies and a new taxonomy of transactional Web services to devise a fault-tolerant mechanism that combines exception handling and transaction techniques. In addition, Liu et al. devise two modules, known as specification and verification, to assist service designers in constructing fault handling logic conveniently and correctly. This logic is automatically injected into WS-BPEL. In the third paper, entitled “Rule-Based Coordination of Distributed Web Service Transactions,” von Riegen et al. study the distributed transactional activity control problem in the context of service choreographies. In such a context, many participants are allowed to work together to achieve a global, common goal, and the initiator of a process is not always the one who is able to commit or cancel a transaction. Von Riegen et al. introduce a framework that allows autonomous coordination of dynamic processes. This framework extends WSBusinessActivity to strengthen the role of the coordinator. Predicate rules are developed to let participants cancel or complete a process and help the coordinators decide on the completion processes and the confirmation or cancellation of the participants’ works. In the fourth paper, entitled “TQoS: Transactional and QoS-Aware Selection Algorithm for Automatic Web Service Composition,” El Haddad et al. focus on the issues of selecting and composing Web services. A design-time selection algorithm is proposed in which transactional and QoS requirements are both integrated into the selection process. This algorithm is based on the notion of risk that indicates if execution outcomes can either be compensated for or not. Two risk levels of execution in a transactional system are considered: Risk 0, meaning that if the execution is successful, the obtained outcomes can be compensated for by the user, and Risk 1, meaning that the system does not guarantee successful execution, but if it achieves it, the outcomes cannot be compensated for by the user. We hope this special section inspires researchers to develop new transactional models that would guarantee service-oriented applications integrity and continuity. 30 IEEE TRANSACTIONS ON SERVICES COMPUTING, VOL. 3, NO. 1, JANUARY-MARCH 2010

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.

Summary form only given. The emerging concept of semantic Web services aims at more sophisticated Web Service technologies: on basis of semantic description frameworks, intelligent mechanisms are envisioned for discovery, composition, and contracting of Web services. The tutorial explains the current state of the art in semantic Web services on basis of the Web service modeling ontology WSMO and related initiatives. Commencing from the vision and arising challenges for semantic Web services, the tutorial in detail explains the specifications of recent frameworks for semantic Web services and presents the Web service execution environment WSMX as the WSMO reference implementation. The tutorial consists of three main sections that subsequently provide a complete overview of semantic Web services and the latest status of WSMO. The tutorial addresses academic as well as industrial researches and developers that are working with Web services and are interested in semantic Web services.

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 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.

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.

An efficient composition of Web services with active network support