1,720,986 research outputs found
A model checking approach to verify BPEL4WS workflows
No full textThe increasing diffusion of service oriented computing in critical business transactions demands reliability and correctness of the workflow logic representing web service orchestrations.
We present an approach for the formal verification of workflow-based compositions of web services, described in BPEL4WS. Workflow processes can be verified in isola- tion, assuming that the external services invoked are known only through their interface. It is also possible to verify that the actual composition of two or more processes behaves correctly. We can verify deadlock freedom, properties expressed as data-bound assertions written in WS-CoL, a specification language for web services, and LTL temporal properties. Our approach is based on the software model checker Bogor, whose language supports the modeling of all BPEL4WS constructs.
We provide an empirical evaluation of our approach and we compare the results with other BPEL4WS model checking tools
Keep it small, keep it real: efficient run-time verification of Web service compositions
No full textService compositions leverage remote services to deliver added-value distributed applications. Since services are administered and run by independent parties, the governance of service compositions is intrinsically decentralized and services may evolve independently over time. In this context, pre-deployment verification can only provide limited guarantees, while continuous run-time verification is needed to probe and guarantee the correctness of compositions at run time.
This paper addresses the issue of efficiency in the run-time verification of service compositions described in BPEL. It considers an existing monitoring approach based on ALBERT, which is a temporal logic language suitable for asserting both functional and non-functional prop- erties, and shows how to obtain the efficient run-time verification of ALBERT formulae. The paper introduces an operational semantics for ALBERT through an extension of alternating automata, and explains how to optimize it to produce smarter, and thus more efficient, encodings of defined formulae. The optimized operational semantics can then be the basis for an efficient implementation of the run-time verification framework
A guided tour through SAVVY-WS: a methodology for specifying and validating web services compositions
No full textService-Oriented Architectures are emerging as a promising solution to the problem of developing distributed and evolvable applications that live in an open world. We contend that developing these applications not only requires adopting a new architectural style, but more generally requires re-thinking the whole life-cycle of an application, from development time through deployment to run time. In particular, the traditional boundary between development time and run time is blurring. Validation, which traditionally pertains to development time, must now extend to run time. In this paper, we provide a tutorial introduction to SAVVY-WS, a methodology that aims at providing a novel integrated approach for design-time and run-time validation. SAVVY-WS has been developed in the context of Web service-based applications, composed via the BPEL workflow language
A timed extension of WSCoL
No full textWeb service based applications are expected to live in dynamically evolving settings. At run-time, services may undergo changes that could modify their expected behavior. Because of such intrinsic dynamic nature, applications should be designed by adhering to the principles of design-by-contract. Run-time monitoring is needed to check that the contract between service providers and service users is fulfilled while the collaboration is in place. We describe a language to specify the expected functional and non-functional requirements that a service provider should fulfill. The language (Timed WSCoL) is a temporal extension of a previous proposal (WSCoL). We also illustrate the ar- chitecture of a run-time analyzer that checks Timed WSCoL properties. Should such properties be disproved during ex- ecution, appropriate recovery and reconfiguration actions may be put in place
Validation of web service compositions
No full textWeb services support software architectures that can evolve dynamically. In particular, in this paper the focus is on architectures where services are composed (orchestrated) through a workflow described in the business process execution language (BPEL). It is assumed that the resulting composite service refers to external services through assertions that specify their expected functional and non-functional properties. On the basis of these assertions, the composite service may be verified at design time by checking that it ensures certain relevant properties. Because of the dynamic nature of web services and the multiple stakeholders involved in their provision, however, the external services may evolve dynamically, and even unexpectedly. They may become inconsistent with respect to the assertions against which the workflow was verified during development. As a consequence, validation of the composition must extend to run time. In this work, an assertion language, called assertion language for BPEL process interactions (ALBERT), is introduced; it can be used to specify both functional and non-functional properties. An environment which supports design-time verification of ALBERT assertions for BPEL workflows via model checking is also described. At run time, the assertions can be turned into checks that a software monitor performs on the composite system to verify that it continues to guarantee its required properties. A TeleAssistance application is provided as a running example to illustrate our validation framework
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Multi-objective low-thrust trajectory optimisation: variable and constant specific impulse
No full textINTERNATIONAL SPACECRAFT PROPULSION CONFERENCE, JUNE 2004, CHIA LAGUNA, SARDEGN
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Multi-Objective Low-Thrust Trajectory Optimization for Constant and Variable Specific Impulse Thrusters
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