A Linear Logic approach to RESTful web service modelling and composition

A thesis submitted to the University of Bedfordshire in partial fulfilment of the requirements for the degree of Doctor of PhilosophyRESTful Web Services are gaining increasing attention from both the service and the Web communities. The rising number of services being implemented and made available on the Web is creating a demand for modelling techniques that can abstract REST design from the implementation in order better to specify, analyse and implement large-scale RESTful Web systems. It can also help by providing suitable RESTful Web Service composition methods which can reduce costs by effi ciently re-using the large number of services that are already available and by exploiting existing services for complex business purposes. This research considers RESTful Web Services as state transition systems and proposes a novel Linear Logic based approach, the first of its kind, for both the modelling and the composition of RESTful Web Services. The thesis demonstrates the capabilities of resource-sensitive Linear Logic for modelling five key REST constraints and proposes a two-stage approach to service composition involving Linear Logic theorem proving and proof-as-process based on the π-calculus. Whereas previous approaches have focused on each aspect of the composition of RESTful Web Services individually (e.g. execution or high-level modelling), this work bridges the gap between abstract formal modelling and application-level execution in an efficient and effective way. The approach not only ensures the completeness and correctness of the resulting composed services but also produces their process models naturally, providing the possibility to translate them into executable business languages. Furthermore, the research encodes the proposed modelling and composition method into the Coq proof assistant, which enables both the Linear Logic theorem proving and the π-calculus extraction to be conducted semi-automatically. The feasibility and versatility studies performed in two disparate user scenarios (shopping and biomedical service composition) show that the proposed method provides a good level of scalability when the numbers of services and resources grow

Web Services Compositions Modelling and Choreographies Analysis

International audienceIn (Rouached, Godart and al. 2006; Rouached, Godart 2007), we have described the semantics of WSBPEL by way of mapping each of the WSBPEL (Arkin, Askary and al. 2004) constructs to the EC algebra and building a model of the process behaviour. With these mapping rules, we have described a modelling approach of a process defined for a single Web service composition. However, this modelling is limited to a local view and can only be used to model the behaviour of a single process. A series of compositions in Web service choreography need specific modelling activities that are not explicitly derived from an implementation. An elaboration of modelling is then required to represent the behaviour of interacting compositions across partnered processes. This elaboration provides a representation that enables us to perform analysis of service interaction for behaviour properties. The ability to perform verification and validation between execution and design, and within the process compositions themselves, is a key requirement of the Web services architecture specification. In this paper, we further the semantic mapping to include Web service composition interactions through modelling Web service conversations and their choreography. We describe this elaboration of models to support a view of interacting Web service compositions extending the mapping from WSBPEL to EC, and including Web service interfaces (WSDL) for use in modelling between services. The verification and validation techniques are also exposed. An automated induction-based theorem prover is used as verification back-end

Automated Runtime Testing of Web Services

Service-oriented computing (SOC) is a relatively new paradigm for developing software applications through the composition of software units called services. With services, software is no longer owned but offered remotely, within or across organisational borders. Currently, the dominant technology for implementing services is that of Web services. Since service requestors do not usually have access to the implementation source code, from their perspective, services are offered as black boxes. However, requestors need to verify first that provided services are trustworthy and implemented correctly before they are integrated into their own business-critical systems. The verification and testing of remote, third-party services involve unique considerations, since testing must be performed in a blackbox manner and at runtime. Addressing the aforementioned concerns, the research work described in this thesis investigates the feasibility of testing Web services for functional correctness, especially at runtime. The aim is to introduce rigour and automation to the testing process, so that service requestors can verify Web services with correctness guarantees and with the aid of tools. Thus, formal methods are utilised to specify the functionality of Web services unambiguously, so that they are amenable to automated and systematic testing. The well-studied stream X-machine (SXM) formalism has been selected as suitable for modelling both the dynamic behavior and static data of Web services, while a proven testing method associated with SXMs is used to derive test sets that can verify the correctness of the implementations. This research concentrates on testing stateful Web services, in which the presence of state makes their behaviour more complex and more difficult to specify and test. The nature of Web service state, its effect on service behaviour, and implications on service modelling and testing, are investigated. In addition, comprehensive techniques are described for deriving a stream X-machine specification of a Web service, and for subsequently testing its implementation for equivalence to the specification. Then, a collaborative approach that makes possible third-party Web service verification and validation is proposed, in which the service provider is required to supply a SXM specification of the service functionality along with the standard WSDL description of its interface. On top of that, techniques are proposed for service providers to include information that ground the abstract SXM specification to the concrete Web service implementation. Having these descriptions available, it is possible to automate at runtime not only test set generation but also test case execution on Web services. A tool has been developed as part of this work, which extends an existing SXM-based testing tool (JSXM). The tool supports the tester activities, consisting of generation of abstract test cases from the SXM specification and their execution on the Web service under test using the supplied grounding information. Practical Web service examples are also used throughout the thesis to demonstrate the proposed techniques

AUTOMATED COMPOSITION OF WEB SERVICES VIA PLANNING IN ASYNCHRONOUS DOMAINS\ud

The service-oriented paradigm promises a novel degree of interoperability between\ud business processes, and is leading to a major shift in way distributed applications are\ud designed and realized. While novel and more powerful services can be obtained, in such\ud setting, by suitably orchestrating existing ones, manually developing such orchestrations\ud is highly demanding, time-consuming and error-prone. Providing automated service\ud composition tools is therefore essential to reduce the time to market of services, and\ud ultimately to successfully enact the service-oriented approach.\ud In this paper, we show that such tools can be realized based on the adoption and extension\ud of powerful AI planning techniques, taking the “planning via model-checking” approach\ud as a stepping stone. In this respect, this paper summarizes and substantially extends a\ud research line that started early in this decade and has continued till now. Specifically, this\ud work provides three key contributions.\ud First, we describe a novel planning framework for the automated composition of Web\ud services, which can handle services specified and implemented using industrial standard\ud languages for business processes modeling and execution, like ws-bpel. Since these\ud languages describe stateful Web services that rely on asynchronous communication\ud primitives, a distinctive aspect of the presented framework is its ability to model and\ud solve planning problems for asynchronous domains.\ud Second, we formally spell out the theory underlying the framework, and provide algorithms\ud to solve service composition in such framework, proving their correctness and\ud completeness. The presented algorithms significantly extend state-of-the-art techniques\ud for planning under uncertainty, by allowing the combination of asynchronous domains\ud according to behavioral requirements.\ud Third, we provide and discuss an implementation of the approach, and report extensive\ud experimental results which demonstrate its ability to scale up to significant cases for\ud which the manual development of ws-bpel composed services is far from trivial and time\ud consuming

Model-driven design, simulation and implementation of service compositions in COSMO

The success of software development projects to a large extent depends on the quality of the models that are produced in the development process, which in turn depends on the conceptual and practical support that is available for modelling, design and analysis. This paper focuses on model-driven support for service-oriented software development. In particular, it addresses how services and compositions of services can be designed, simulated and implemented. The support presented is part of a larger framework, called COSMO (COnceptual Service MOdelling). Whereas in previous work we reported on the conceptual support provided by COSMO, in this paper we proceed with a discussion of the practical support that has been developed. We show how reference models (model types) and guidelines (design steps) can be iteratively applied to design service compositions at a platform independent level and discuss what tool support is available for the design and analysis during this phase. Next, we present some techniques to transform a platform independent service composition model to an implementation in terms of BPEL and WSDL. We use the mediation scenario of the SWS challenge (concerning the establishment of a purchase order between two companies) to illustrate our application of the COSMO framework

Semantic model-driven development of web service architectures.

Building service-based architectures has become a major area of interest since the advent of Web services. Modelling these architectures is a central activity. Model-driven development is a recent approach to developing software systems based on the idea of making models the central artefacts for design representation, analysis, and code generation. We propose an ontology-based engineering methodology for semantic model-driven composition and transformation of Web service architectures. Ontology technology as a logic-based knowledge representation and reasoning framework can provide answers to the needs of sharable and reusable semantic models and descriptions needed for service engineering. Based on modelling, composition and code generation techniques for service architectures, our approach provides a methodological framework for ontology-based semantic service architecture

Distribution pattern-driven development of service architectures

Distributed systems are being constructed by composing a number of discrete components. This practice is particularly prevalent within the Web service domain in the form of service process orchestration and choreography. Often, enterprise systems are built from many existing discrete applications such as legacy applications exposed using Web service interfaces. There are a number of architectural configurations or distribution patterns, which express how a composed system is to be deployed in a distributed environment. However, the amount of code required to realise these distribution patterns is considerable. In this paper, we propose a distribution pattern-driven approach to service composition and architecting. We develop, based on a catalog of patterns, a UML-compliant framework, which takes existing Web service interfaces as its input and generates executable Web service compositions based on a distribution pattern chosen by the software architect

Quality-aware model-driven service engineering

Service engineering and service-oriented architecture as an integration and platform technology is a recent approach to software systems integration. Quality aspects ranging from interoperability to maintainability to performance are of central importance for the integration of heterogeneous, distributed service-based systems. Architecture models can substantially influence quality attributes of the implemented software systems. Besides the benefits of explicit architectures on maintainability and reuse, architectural constraints such as styles, reference architectures and architectural patterns can influence observable software properties such as performance. Empirical performance evaluation is a process of measuring and evaluating the performance of implemented software. We present an approach for addressing the quality of services and service-based systems at the model-level in the context of model-driven service engineering. The focus on architecture-level models is a consequence of the black-box character of services