Correctness of services and their composition

We study correctness of services and their composition and investigate how the design of correct service compositions can be systematically supported. We thereby focus on the communication protocol of the service and approach these questions using formal methods and make contributions to three scenarios of SOC.Wir studieren die Korrektheit von Services und Servicekompositionen und untersuchen, wie der Entwurf von korrekten Servicekompositionen systematisch unterstützt werden kann. Wir legen dabei den Fokus auf das Kommunikationsprotokoll der Services. Mithilfe von formalen Methoden tragen wir zu drei Szenarien von SOC bei

Correctness of services and their composition

We study correctness of services and their composition and investigate how the design of correct service compositions can be systematically supported. We thereby focus on the communication protocol of the service and approach these questions using formal methods and make contributions to three scenarios of SOC.Wir studieren die Korrektheit von Services und Servicekompositionen und untersuchen, wie der Entwurf von korrekten Servicekompositionen systematisch unterstützt werden kann. Wir legen dabei den Fokus auf das Kommunikationsprotokoll der Services. Mithilfe von formalen Methoden tragen wir zu drei Szenarien von SOC bei

A correct-by-construction model for asynchronously communicating systems

The design and verification of distributed software systems is often hindered by their ever-increasing complexity and their asynchronous operational semantics. This article considers choreography specifications for distributed systems to reduce that complexity. We use labelled state-transitions systems as ground model for both choreographies and the corresponding distributed systems. Based on Event-B method, we propose a stepwise correct-by-construction model to build asynchronous distributed systems which a priori realise their choreographies. We rely on a sufficient and necessary realisability condition and we apply several refinement steps w.r.t. that condition to generate the distributed peers. The first refinement returns peer behaviours obtained by synchronous projection. The previously computed system is then refined into its asynchronous version using unbounded FIFO buffers. We prove, thanks to invariant preservation, that a sequence of exchanged messages is preserved at each refinement step. We provide a formalised proof of a realisability algorithm for deterministic choreographies. Besides that, our contribution is twofold: the approach is a priori and the problackposed solution scales up to any number of peers communicating with each other

Locally Static, Globally Dynamic Session Types for Active Objects

Active object languages offer an attractive trade-off between low-level, preemptive concurrency and fully distributed actors: syntactically identifiable atomic code segments and asynchronous calls are the basis of cooperative concurrency, still permitting interleaving, but nevertheless being mechanically analyzable. The challenge is to reconcile local static analysis of atomic segments with the global scheduling constraints it depends on. Here, we propose an approximate, hybrid approach; At compile-time we perform a local static analysis: later, any run not complying to a global specification is excluded via runtime checks. That specification is expressed in a type-theoretic language inspired by session types. The approach reverses the usual (first global, then local) order of analysis and, thereby, supports analysis of open distributed systems

Stability of Asynchronously Communicating Systems

Recent software is mostly constructed by reusing and composing existing components. Software components are usually stateful and therefore described using behavioral models such as finite state machines. Asynchronous communication is a classic interaction mechanism used for such software systems. However, analysing communicating systems interacting asynchronously via reliable FIFO buffers is an undecidable problem. A typical approach is to check whether the system is bounded, and if not, the corresponding state space can be made finite by limiting the presence of communication cycles in behavioral models or by fixing buffer sizes. In this paper, we focus on infinite systems and we do not restrict the system by imposing any arbitrary bounds. We introduce a notion of stability and prove that once the system is stable for a specific buffer bound, it remains stable whatever larger bounds are chosen for buffers. This enables us to check certain properties on the system for that bound and to ensure that the system will preserve them whatever larger bounds are used for buffers. We also prove that computing this bound is undecidable but show how we succeed in computing these bounds for many typical examples using heuristics and equivalence checking

Changing Time - Shaping World

A World of Changemakers - how can a hybrid arts lecture series concept in e-learning create attitudes and shape skills as a playful and critical thinking navigator in an uncertain world? To re-create meaning is an interdisciplinary cross-sectional task of our zeitgeist in a civil society. The international contributors represent key roles in relevant philosophical, technical or economic debates, non-university community art & design projects or companies

Changing Time - Shaping World: Changemakers in Arts & Education

A World of Changemakers - how can a hybrid arts lecture series concept in e-learning create attitudes and shape skills as a playful and critical thinking navigator in an uncertain world? To re-create meaning is an interdisciplinary cross-sectional task of our zeitgeist in a civil society. The international contributors represent key roles in relevant philosophical, technical or economic debates, non-university community art & design projects or companies

Changing Time - Shaping World

A World of Changemakers - how can a hybrid arts lecture series concept in e-learning create attitudes and shape skills as a playful and critical thinking navigator in an uncertain world? To re-create meaning is an interdisciplinary cross-sectional task of our zeitgeist in a civil society. The international contributors represent key roles in relevant philosophical, technical or economic debates, non-university community art & design projects or companies

GUISET: A CONCEPTUAL DESIGN OF A GRID-ENABLED PORTAL FOR E-COMMERCE ON-DEMAND SERVICES

Conventional grid-enabled portal designs have been largely influenced by the usual functional requirements such as security requirements, grid resource requirements and job management requirements. However, the pay-as-you-use service provisioning model of utility computing platforms mean that additional requirements must be considered in order to realize effective grid-enabled portals design for such platforms. This work investigates those relevant additional requirements that must be considered for the design of grid-enabled portals for utility computing contexts. Based on a thorough review of literature, we identified a number of those relevant additional requirements, and developed a grid-enabled portal prototype for the Grid-based Utility Infrastructure for SMME-enabling Technology (GUISET) initiative – a utility computing platform. The GUISET portal was designed to cater for both the traditional grid requirements and some of the relevant additional requirements for utility computing contexts. The result of the evaluation of the GUISET portal prototype using a set of benchmark requirements (standards) revealed that it fulfilled the minimum requirements to be suitable for the utility context