54 research outputs found

    Analysis of communication models in web service compositions

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    In this paper we describe an approach for the verification of Web service compositions dened by sets of BPEL processes. The key aspect of such a verification is the model adopted for representing the communications among the services participating in the composition. Indeed, these communications are asynchronous and buffered in the existing execution frameworks, while most verication approaches assume a synchronous communication model for efficiency reasons. In our approach, we develop a parametric model for describing Web service compositions, which allows us to capture a hierarchy of communication models, ranging from synchronous communications to asynchronous communications with complex buffer structures. Moreover, we develop a technique to associate with a Web service composition the most adequate communication model, i.e., the simplest model that is sufficient to capture all the behaviors of the composition. This way, we can provide an accurate model of a wider class of service composition scenarios, while preserving as much as possible an efficient performance in verification

    Recovery within long running transactions

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    As computer systems continue to grow in complexity, the possibilities of failure increase. At the same time, the increase in computer system pervasiveness in day-to-day activities brought along increased expectations on their reliability. This has led to the need for effective and automatic error recovery techniques to resolve failures. Transactions enable the handling of failure propagation over concurrent systems due to dependencies, restoring the system to the point before the failure occurred. However, in various settings, especially when interacting with the real world, reversal is not possible. The notion of compensations has been long advocated as a way of addressing this issue, through the specification of activities which can be executed to undo partial transactions. Still, there is no accepted standard theory; the literature offers a plethora of distinct formalisms and approaches. In this survey, we review the compensations from a theoretical point of view by: (i) giving a historic account of the evolution of compensating transactions; (ii) delineating and describing a number of design options involved; (iii) presenting a number of formalisms found in the literature, exposing similarities and differences; (iv) comparing formal notions of compensation correctness; (v) giving insights regarding the application of compensations in practice; and (vi) discussing current and future research trends in the area.peer-reviewe

    A compensating transaction example in twelve notations

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    The scenario of business computer systems changed with the advent of cross-entity computer interactions: computer systems no longer had the limited role of storing and processing data, but became themselves the players which actuated real-life actions. These advancements rendered the traditional transaction mechanism insufficient to deal with these new complexities of longer multi-party transactions. The concept of compensations has long been suggested as a solution, providing the possibility of executing “counter”-actions which semantically undo previously completed actions in case a transaction fails. There are numerous design options related to compensations particularly when deciding the strategy of ordering compensating actions. Along the years, various models which include compensations have emerged, each tackling in its own way these options. In this work, we review a number of notations which handle compensations by going through their syntax and semantics — highlighting the distinguishing features — and encoding a typical compensating transaction example in terms of each of these notations.peer-reviewe

    Automated synthesis of composite BPEL4WS Web services

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    In this paper we propose a technique for the automated synthesis of new composite web services. Given a set of ab-stract BPEL4WS descriptions of component services, and a composition requirement, we automatically generate an ex-ecutable BPEL4WS process that, once deployed, is able to interact with the components to satisfy the requirement. We implement the proposed approach exploiting efficient syn-thesis techniques, and experiment with some case studies taken from real world applications and with a parameter-ized domain. We show that the technique can scale up to cases in which the manual development of BPEL4WS com-posite services is not trivial and is time consuming.

    Formalising workflow: A CCS-inspired characterisation of the YAWL workflow patterns

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    Specifying and Verifying Contract-driven Composite Web Services: a Model Checking Approach

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    As a promising computing paradigm in the new era of cross-enterprise e-applications, web services technology works as plugin mode to provide a value-added to applications using Service-Oriented Computing (SOC) and Service-Oriented Architecture (SOA). Verification is an important issue in this paradigm, which focuses on abstract business contracts and where services’ behaviors are generally classified in terms of compliance with / violation of their contracts. However, proposed approaches fail to describe in details both compliance and violation behaviors, how the system can distinguish between them, and how the system reacts after each violation. In this context, specifying and automatically generating verification properties are challenging key issues. This thesis proposes a novel approach towards verifying the compliance with contracts regulating the composition of web services. In this approach, properties against which the system is verified are generated automatically from the composition’s implementation. First, Business Process Execution Language (BPEL)that specifies actions within business processes with web services is extended to create custom activities, called labels. Those labels are used as means to represent the specifications and mark the points the developer aims to verify. A significant advantage of this labeling is the ability to target specific points in the design to be verified, which makes this verification very focused. Second, new translation rules from the extended BPEL into ISPL, the input language of the MCMAS model checker, are provided so that model checking the behavior of our contract-driven compositions is possible. The verification properties are expressed in the CTLC logic, which provides a powerful representation for modeling composition contracts using commitment-based multiagent interactions. A detailed case study with experimental results are also reported ins the thesis

    Using formal methods to develop WS-BPEL applications

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    In recent years, WS-BPEL has become a de facto standard language for orchestration of Web Services. However, there are still some well-known difficulties that make programming in WS-BPEL a tricky task. In this paper, we firstly point out major loose points of the WS-BPEL specification by means of many examples, some of which are also exploited to test and compare the behaviour of three of the most known freely available WS-BPEL engines. We show that, as a matter of fact, these engines implement different semantics, which undermines portability of WS-BPEL programs over different platforms. Then we introduce Blite, a prototypical orchestration language equipped with a formal operational semantics, which is closely inspired by, but simpler than, WS-BPEL. Indeed, Blite is designed around some of WS-BPEL distinctive features like partner links, process termination, message correlation, long-running business transactions and compensation handlers. Finally, we present BliteC, a software tool supporting a rapid and easy development of WS-BPEL applications via translation of service orchestrations written in Blite into executable WS-BPEL programs. We illustrate our approach by means of a running example borrowed from the official specification of WS-BPEL

    A programming system for process coordination in virtual organisations

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    PhD thesisDistributed business applications are increasingly being constructed by composing them from services provided by various online businesses. Typically, this leads to trading partners coming together to form virtual organizations (VOs). Each member of a VO maintains their autonomy, except with respect to their agreed goals. The structure of the Virtual Organisation may contain one dominant organisation who dictates the method of achieving the goals or the members may be considered peers of equal importance. The goals of VOs can be defined by the shared global business processes they contain. To be able to execute these business processes, VOs require a flexible enactment model as there may be no single ‘owner’ of the business process and therefore no natural place to enact the business processes. One solution is centralised enactment using a trusted third party, but in some cases this may not be acceptable (for instance because of security reasons). This thesis will present a programming system that allows centralised as well as distributed enactment where each organisation enacts part of the business process. To achieve distributed enactment we must address the problem of specifying the business process in a manner that is amenable to distribution. The first contribution of this thesis is the presentation of the Task Model, a set of languages and notations for describing workflows that can be enacted in a centralised or decentralised manner. The business processes that we specify will coordinate the services that each organisation owns. The second contribution of this thesis is the presentation of a method of describing the observable behaviour of these services. The language we present, SSDL, provides a flexible and extensible way of describing the messaging behaviour of Web Services. We present a method for checking that a set of services described in SSDL are compatible with each other and also that a workflow interacts with a service in the desired manner. The final contribution of this thesis is the presentation of an abstract architecture and prototype implementation of a decentralised workflow engine. The prototype is able to enact workflows described in the Task Model notation in either a centralised or decentralised scenario

    FORMAL ANALYSIS OF WEB SERVICE COMPOSITION

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    Ph.DDOCTOR OF PHILOSOPH
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