Abstractions and Static Analysis for Verifying Reactive Systems

Fokkink, W.J. [Promotor]Sidorova, N. [Copromotor

Analytical performance evaluation of concurrent communicating systems using SLD and stochastic Petri nets

Bibliography: leaves 113-117.In this thesis, the performance analysis of SDL with a new type of stochastic Petri net is described. This new net is called SDL-net. The Concurrent Communicating System is described, and the need for qualitative and quantitative analysis of such systems is motivated. Formal methods are demonstrated which can be used to represent such Concurrent Communicating Systems. The Specification and Description Language (SDL) is shown in the context of Concurrent Communicating Systems and the software development cycle is described for SDL systems. Correctness and performance of SDL are discussed and it is shown how the semantics of time for performance can be introduced into SDL by adding external information, by extending the SDL syntax or by using compiler directives. In this thesis only external information is added

Distributed Real-time Systems - Deterministic Protocols for Wireless Networks and Model-Driven Development with SDL

In a networked system, the communication system is indispensable but often the weakest link w.r.t. performance and reliability. This, particularly, holds for wireless communication systems, where the error- and interference-prone medium and the character of network topologies implicate special challenges. However, there are many scenarios of wireless networks, in which a certain quality-of-service has to be provided despite these conditions. In this regard, distributed real-time systems, whose realization by wireless multi-hop networks becomes increasingly popular, are a particular challenge. For such systems, it is of crucial importance that communication protocols are deterministic and come with the required amount of efficiency and predictability, while additionally considering scarce hardware resources that are a major limiting factor of wireless sensor nodes. This, in turn, does not only place demands on the behavior of a protocol but also on its implementation, which has to comply with timing and resource constraints. The first part of this thesis presents a deterministic protocol for wireless multi-hop networks with time-critical behavior. The protocol is referred to as Arbitrating and Cooperative Transfer Protocol (ACTP), and is an instance of a binary countdown protocol. It enables the reliable transfer of bit sequences of adjustable length and deterministically resolves contest among nodes based on a flexible priority assignment, with constant delays, and within configurable arbitration radii. The protocol's key requirement is the collision-resistant encoding of bits, which is achieved by the incorporation of black bursts. Besides revisiting black bursts and proposing measures to optimize their detection, robustness, and implementation on wireless sensor nodes, the first part of this thesis presents the mode of operation and time behavior of ACTP. In addition, possible applications of ACTP are illustrated, presenting solutions to well-known problems of distributed systems like leader election and data dissemination. Furthermore, results of experimental evaluations with customary wireless transceivers are outlined to provide evidence of the protocol's implementability and benefits. In the second part of this thesis, the focus is shifted from concrete deterministic protocols to their model-driven development with the Specification and Description Language (SDL). Though SDL is well-established in the domain of telecommunication and distributed systems, the predictability of its implementations is often insufficient as previous projects have shown. To increase this predictability and to improve SDL's applicability to time-critical systems, real-time tasks, an approved concept in the design of real-time systems, are transferred to SDL and extended to cover node-spanning system tasks. In this regard, a priority-based execution and suspension model is introduced in SDL, which enables task-specific priority assignments in the SDL specification that are orthogonal to the static structure of SDL systems and control transition execution orders on design as well as on implementation level. Both the formal incorporation of real-time tasks into SDL and their implementation in a novel scheduling strategy are discussed in this context. By means of evaluations on wireless sensor nodes, evidence is provided that these extensions reduce worst-case execution times substantially, and improve the predictability of SDL implementations and the language's applicability to real-time systems

Nutzerfreundliche Modellierung mit hybriden Systemen zur symbolischen Simulation in CLP

Die Dissertation beinhaltet die Sprachen MODEL-HS und VYSMO zur modularen, deklarativen Beschreibung hybrider Systeme, die dem Nachweis zeit- und sicherheitskritischer Eigenschaften für die symbolische Simulation in CLP dienen. Zum Erlangen sprachtheoretischer Erkenntnisse wie Entscheidbarkeit wurden hybride Systeme neu unter formal nachweisbaren Akzeptanzbedingungen definiert, welche durch praktische Beispiele belegt sind. Weitere Ergebnisse sind eine neue Klassifikation hybrider Systeme, ein Werkzeug ROSSY, Anfragebeschreibungen und deren Transformation in temporal-logische Ausdrücke, Anfragemasken und Anwendungen für Studiensysteme und parallele Programme.The dissertation includes the languages MODEL-HS and VYSMO for modular, declarative description of hybrid systems that serve the proof of time- and safety-critical properties for symbolic simulation in CLP. For coming to language-theoretical conclusions like decidability hybrid systems are newly defined under acceptance conditions that can be formally proved and for which practical examples bear witness. A new classification of hybrid systems, a tool ROSSY, query descriptions and their transformation into temporal-logic expressions, query forms and applications for study systems and parallel programs are further results

Third Workshop and Tutorial on Practical Use of Coloured Petri Nets and the CPN Tools, Aarhus, Denmark, August 29-31, 2001

This booklet contains the proceedings of the Third Workshop on Practical Use of Coloured Petri Nets and the CPN Tools, August 29-31, 2001. The workshop is organised by the CPN group at Department of Computer Science, University of Aarhus, Denmark. The papers are also available in electronic form via the web pages: http://www.daimi.au.dk/CPnets/workshop01

Adaptable service-system design: an analysis of Shariah finance in Pakistan

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.An adaptable service system adjusts to the operational-level environments of organisations to enable heterogeneous services. This adaptation is important for sustainability and contextual-value (benefit) creation in a service system. Academics, such as those related to the current service-ecosystem concept, acknowledge the significance of this adaptation. However, little is known about a comprehensive adaptation process and how that integrates within a design for a service system. Also, practitioners are inclined towards this development, as the financial regulator in Pakistan has established an “evolutionary framework”. This framework encourages financial institutions to design Shariah finance services (SFS) which respond and evolve to the emergent market environments. The existing SFS models take benefit from Islamic jurisprudence and economics literatures to provide designs for transactions of financial and physical assets. However, the SFS models de-emphasis the intangible service-elements, where the adaptation is more likely to occur. Currently there is a great need for models that could explain the detailed adaptation process and its placement in an SFS design. The aim of this research is to develop, evaluate and theorise a model for conceptualising a holistic adaptable service-system design. The research aim is achieved through the proposal of a novel deferred service-system design (DSD) model. The DSD conceptualises a service-system design that adapts to the operational-level environments of SFS organisations in Pakistan. The DSD has seven constructs: (i) the service creators apply centrally-planned designs to create a service ii) they adapt these designs to meet the requirements of emergent contexts (iii) the service personnel, customers and aiding parties co-create a service by integrating their (iv) roles and actions, (v) resources and usufructs, (vi) rules and control to generate (vii) value. DSD is based on service-system design (SSD) literature, SFS literature and theory of deferred action (TODA) a theory of system and organisation design. A multiple case study strategy is employed to evaluate, extend and theorise the DSD developed in phase I. Qualitative data are collected in four SFS organisations: Islamic commercial bank, Islamic life Takaful, Islamic mutual fund, and Islamic leasing organisation. Thirty-two in-depth narrative interviews of SFS personnel are conducted and analysed using a narrative discourse analysis method. The findings are triangulated by adding focus-group discussions, visualisations and service offering documents. The empirical findings are synthesised with the extant literature to develop a novel and comprehensive DSD in phase II. The findings show that the service co-creators apply a centrally-developed planned design typology (PDT). PDT includes different blends of SFS models (e.g., partnerships, sales, leases, agency and endowment), expected varieties (list, range and negative) and addable-deductible modules. The service co-creators and their inclusive systems (e.g., families, societies, markets, regulators and other government agencies) affect the planned service-system design to adapt or migrate. The service co-creators follow a novel six-step deferred adaptation process (DAP): emergence locale, information diffusion, knowledge diffusion, indexation, specifics evaluation and adaptation/migration. The empirical findings advance our understanding of a service-system design by showing how a planned design enables adaptation through PDT. More importantly, how the service co-creators follow a systematic process, DAP, to attain the desired adaptation or migrate off the scene. The findings also broaden the conceptualisation of SFS by showing how it is co-created by the financial institutions, customers and aiding parties. This is due to the SFS being perceived as a product of financial institution alone. This research also makes a contribution to service visualisation method by extending and using the service blueprint as an additional data-collection and analysis tool. This study provided fourteen implications for the practitioners.Government in Pakistan, the Higher Education Commission of Pakistan and the Institute of Management Sciences, Peshawar Pakistan

Entwurfsbegleitende Leistungsanalyse für SDL-basiertes Design multimedialer Internet-Transportsysteme

Neben der funktionalen Korrektheit von komplexen Kommunikationssystemen spielt eine ausreichende Performance dieser Systeme eine immer wichtigere Rolle. Dabei ist es notwendig, Performance-Aspekte bereits in frühen Entwurfsphasen und nicht erst nach der Implementierung der Systeme zu berücksichtigen. Die vorliegende Arbeit präsentiert eine Methodik zur entwurfsbegleitenden, modellgestützten Leistungsanalyse von Kommunikationsprotokollen, die mit Hilfe der Sprache SDL formal spezifiziert wurden. Die vorgestellte Methodik verwendet dazu Beschreibungsmechanismen, Verfahren und Werkzeuge, die bereits im Entwurfsprozeß dieser Systeme verwendet werden. Für die wichtigsten Implementierungsansätze von Kommunikationsprotokollen werden Performance-Bausteine vorgestellt und deren Verwendung erläutert. Die Tragfähigkeit der entwickelten Methodik wird durch eine große Fallstudie im Kontext von Reservierungsprotokollen zur Unterstützung von Multimedia-Anwendungen im Internet demonstriert. Dabei werden nicht nur die informellen Angaben der vorhandenen RFCs in formale SDL-Beschreibungen umgesetzt, sondern auch als existent vorausgesetzte Ressource-Management-Funktionen entwickelt und analysiert. Die vorliegende Arbeit schließt so die bisher bestehende Lücke im SDL-basierten Entwurfsprozeß verteilter reaktiver Systeme und ermöglicht die modellgestützte Betrachtung von Performance-Aspekten in den frühen Phasen des Entwurfsprozesses