Cette thèse présente un nouveau modèle temporisé appelé timed-pNets pour la modélisation et la vérification des comportements des systèmes distribués hétérogènes. Un défi essentiel de ces systèmes est de spécifier correctement les contraintes de temps du système, dans la mesure où les nœuds dans les systèmes distribués n'ont pas l'horloge physique commune. Timed-pNets utilise un modèle de temps basé sur des horloges logiques, de manière à ce que les mesures de temps dans ce modèle ne reposent pas sur une horloge physique commune. Les timed-pNets ont une structure hiérarchique en arbre: les feuilles de cet arbre sont des Systèmes de Transition Étiquetés paramétrés temporisés (timed-LTSs), et les autres nœuds sont des dispositifs de synchronisation qui permettent de composer les comportements de leurs sous-réseaux. A chaque nœud d'un timed-pNet peut être associée une spécification temporisée, qui consiste en un ensemble d’horloges logiques et de relations sur ces horloges. Les spécifications temporisées sont utilisées pour spécifier les comportements du système, y compris les communications synchrones et asynchrones. Grâce à la spécification temporisée, les timed-pNets peuvent modéliser des systèmes de manière flexible. Les analyses des limites de temps, de la sûreté et de la latence sont discutées par l'étude des conflits de relations entre les horloges logiques du système. Nous utilisons un scénario d'insertion de voitures dans les systèmes de transport intelligents (ITS) comme un exemple pour illustrer l'utilisation de notre modèle timed-pNets. Finalement, l'outil TimeSquare est utilisé pour effectuer une simulation logique et vérifier la validité de notre modèle. / This thesis presents a novel timed model called timed-pNets for modeling and verifying the communication behaviours of heterogeneous distributed systems. Since the nodes in distributed systems have no common physical clock, it brings the challenges of correctly specifying the system time constraints. Timed-pNets build the time model on top of logical clocks such that the time of this model does not rely on a common physical clock. Timed-pNets are tree style hierarchical structures. Each node is associated with a timed specification which consists of a set of logical clocks and some relations on these clocks. The leaves are represented by timed Parametrized Label Transition Systems (timed-pLTSs). Non-leaf nodes (called timed-pNets nodes) are synchronisation devices that synchronize the behaviours of subnets (these subnets can be leaves or non-leaf nodes). Both timed-pLTSs and timed-pNets nodes can be translated to timed specifications. Timed specifications are designed to specify the system behaviours including synchronous and asynchronous communications. Thanks to the timed specification, timed-pNets are able to model systems in a flexible way. Time bound analysis, safety and latency properties are discussed by investigating the relations conflicts between system logical clocks. We take a simple case of car insertion from the area of Intelligent Transportation Systems (ITS) as an example to demonstrate the use of the timed-pNets model. In the end, the TimeSquare tool is used to perform a logical simulation and check the validity of our model.

Includes vita. / Title from PDF of title page. / Document formatted into pages; contains 323 pages. / Thesis (Ph.D.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: Peer response in which students work together in dyads or small groups to critique and provide feedback on one another's writing is compatible with communicative approaches to foreign language teaching and process approaches to the teaching of writing. Computer-mediated communication has been considered a viable tool for both the teaching of languages and the teaching of writing. There is, however, scant information on how computer-mediated peer response functions in the foreign language classroom. This dissertation investigated how college Spanish learners provided feedback to their peers and the impact of feedback on revision. It also examined the factors that influenced how students wrote their comments, and how they perceived the use of computers for peer response. Case study methodology was used to collect and analyze data from two writing tasks performed as part of a semester-long course. / ABSTRACT: Data sources consisted of written feedback, first and second drafts, interview transcripts, learning journals from 12 participants and the teacher-researcher field notes. Analysis of data indicated that peer response is a complex event, influenced by a variety of contextual factors. Results also indicated that the participants used feedback depending on their needs. Students used reacting, advising and announcing language functions when providing feedback, and focused mostly on content. The revisions made by the participants contradicted the idea that peer feedback directly influences revision; more than half of the revisions made by the participants originated in the writers themselves and not in the suggestions given by their peers. Analysis of the revisions made, based on peers' suggestions indicated that the impact of peer response was strong on the length of the essays, limited on their language below the clause level, and weak on the essays' communicative purpose. / ABSTRACT: The participants' language proficiency and the characteristics of the writing task were perceived by the participants as factors that influenced how they wrote feedback for their peers. Finally, although the students considered that using the word processing language tools allowed them to learn about language and focus on content, the role of technology was perceived as supplementary to oral peer response / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

[pt] Novos contextos da computação distribuída reforçam a necessidade de abstra ções de programação que favoreçam a comunicação assíncrona e o tratamento de tarefas concorrentes. Modelos de programação dirigido a eventos ou baseado em threads incorporam decisões sobre como tratar essas questões, em cada caso apresentando vantagens e desvantagens. Normalmente, a opção pelo modelo mais adequado para um determinado contexto ou problema exige que o programador lide diretamente com as desvantagens inerentes a esse modelo, tornando a tarefa de desenvolvimento de aplicações mais complexa. Nesse trabalho aprofundamos a discussão sobre como combinar as vantagens dos modelos tradicionais de programação para oferecer uma interface de programação mais simples para o programador. Exploramos o uso de operações de comunicação não- bloqueante e de um mecanismo básico de gerência cooperativa de tarefas baseado na construção de co-rotinas. Usando esses conceitos implementamos: (1) um conjunto de operações que facilitam o desenvolvimento de aplicações com a estrutura cliente/servidor sobre uma base de comunicação assíncrona; e (2) uma interface de programação mais apropriada para o TinyOS, o estado da arte em sistema operacional para redes de sensores. / [en] New contexts of distributed computing emphasize the need of programming abstractions able to deal with asynchronous communication and concurrent tasks. Event-driven or threaded programming models are able to deal with these issues, but each model presents particular advantages and problems. Normally, when choosing the model more appropriate for a context or problem, the programmer must deal directly with the difficulties related to this model, making the development task more complex. In this work we discuss a way to combine the advantages of the traditional programming models in order to support a programming interface more suitable for the programmer.We explore asynchronous communication and cooperative task management based on the co-routine construction. By using these concepts, we implement: (1) a set of operations for building client/server applications upon an asynchronous communication basis; and (2) a more appropriate programming interface for TinyOS, the state of the art of operating system for sensor networks.

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Peer response in which students work together in dyads or small groups to critique and provide feedback on one another's writing is compatible with communicative approaches to foreign language teaching and process approaches to the teaching of writing. Computer-mediated communication has been considered a viable tool for both the teaching of languages and the teaching of writing. There is, however, scant information on how computer-mediated peer response functions in the foreign language classroom. This dissertation investigated how college Spanish learners provided feedback to their peers and the impact of feedback on revision. It also examined the factors that influenced how students wrote their comments, and how they perceived the use of computers for peer response. Case study methodology was used to collect and analyze data from two writing tasks performed as part of a semester-long course. Data sources consisted of written feedback, first and second drafts, interview transcripts, learning journals from 12 participants and the teacher-researcher field notes. Analysis of data indicated that peer response is a complex event, influenced by a variety of contextual factors. Results also indicated that the participants used feedback depending on their needs. Students used reacting, advising and announcing language functions when providing feedback, and focused mostly on content. The revisions made by the participants contradicted the idea that peer feedback directly influences revision; more than half of the revisions made by the participants originated in the writers themselves and not in the suggestions given by their peers. Analysis of the revisions made, based on peers' suggestions indicated that the impact of peer response was strong on the length of the essays, limited on their language below the clause level, and weak on the essays' communicative purpose. The participants' language proficiency and the characteristics of the writing task were perceived by the participants as factors that influenced how they wrote feedback for their peers. Finally, although the students considered that using the word processing language tools allowed them to learn about language and focus on content, the role of technology was perceived as supplementary to oral peer response.

Les systèmes informatiques sont construits par composition de plusieurs sous-systèmes répartis. La manière dont communiquent ces entités, ou pairs, joue un rôle clé dans la bonne marche du système composé. L'étude détaillée de ces interactions est donc essentielle dans le cadre de la vérification et du développement formel de tels systèmes. Ces interactions se décomposent en deux catégories: la communication synchrone et la communication asynchrone. La communication synchrone admet une transmission instantanée de l'information, le message, entre deux entités. La communication asynchrone, en revanche, prend en compte le découplage de la transmission du message en une opération d'envoi puis de réception avec la possibilité que des événements s'intercalent entre les deux donnant ainsi lieu à des variations de comportement, désirables ou non, des systèmes. Souvent considérée comme une entité monolithique duale du monde synchrone, le monde asynchrone se décline en réalité en de multiples modèles qui peuvent induire sur la communication une grande variété de propriétés qu'il convient de caractériser et comparer. Cette thèse se focalise sur les modèles de communication qui orchestrent l'ordre de délivrance des messages : par exemple les modèles dits FIFO qui assurent que certains messages sont reçus dans l'ordre dans lequel ils ont été émis. Nous considérons des modèles de communication classiques de la littérature ainsi que des variations de ces modèles dont nous explicitons les différences parfois négligées. Dans un premier temps nous proposons une formalisation logique abstraite et homogène des modèles de communication considérés et nous les hiérarchisons en étendant des résultats existants. Nous proposons dans un second temps une approche opérationnelle sous forme d'un outil de vérification de compositions de pairs que nous mécanisons à l'aide du langage de spécification TLA+ et du vérificateur de modèles TLC. Cet outil permet de spécifier des pairs communicants et des propriétés temporelles à vérifier pour les différents modèles de communication de façon modulaire. Pour cela, nous apportons un ensemble de spécifications uniformes et opérationnelles des modèles de communication basé sur la notion d'histoires de messages. Nous identifions et prouvons les conditions de leur conformité aux définitions logiques et validons ainsi la pertinence de notre outil. Dans un troisième temps nous considérons des spécifications concrètes de nos modèles de communication, semblables à nombre de celles présentes dans la littérature. Nous disposons donc d'une hiérarchisation des modèles selon les propriétés d'ordre qu'ils garantissent mais également d'une autre hiérarchisation pour un modèle donné entre sa définition logique abstraite et ses implantations concrètes. Ces deux dimensions correspondent à deux dimensions du raffinement. Nous introduisons graduellement par raffinement la notion de communication asynchrone point à point et prouvons, grâce à la méthode Event-B, tous les liens de raffinement entre les différents modèles de communication et leurs déclinaisons. Nous offrons ainsi une cartographie détaillée des modèles pouvant être utilisée pour en développer de nouveaux ou identifier les modèles les plus adaptés à des besoins donnés. Enfin, nous proposons des pistes d'extension de nos travaux à la communication par diffusion où un message peut être envoyé simultanément à plusieurs destinataires. En particulier, nous montrons les différences induites dans la hiérarchie des modèles et les adaptations à effectuer sur notre outil de vérification pour prendre en compte ce mode de communication / Large computing systems are generally built by connecting several distributed subsystems. The way these entities communicate is crucial to the proper functioning of the overall composed system. An in-depth study of these interactions makes sense in the context of the formal development and verification of such systems. The interactions fall in two categories: synchronous and asynchronous communication. In synchronous communication, the transmission of a piece of information - the message - is instantaneous. Asynchronous communication, on the other hand, splits the transmission in a send operation and a receive operation. This make the interleaving of other events possible and lead to new behaviours that may or may not be desirable. The asynchronous world is often viewed as a monolithic counterpart of the synchronous world. It actually comes in multiple models that provide a wide range of properties that can be studied and compared. This thesis focuses on communication models that order the delivery of messages: for instance, the "FIFO" models ensure that some messages are received in the order of their emission. We consider classic communication models from the literature as well as a few variations. We highlight the differences that are sometimes overlooked. First, we propose an abstract, logical, and homogeneous formalisation of the communication models and we establish a hierarchy that extends existing results. Second, we provide an operational approach with a tool that verifies the compatibility of compositions of peers. We mechanise this tool with the TLA+ specification language and its model checker TLC. The tool is designed in a modular fashion: the commmunicating peers, the temporal compatibility properties, and the communication models are specified independently. We rely on a set of uniform operational specifications of the communication models that are based on the concept of message history. We identify and prove the conditions under which they conform to the logical definitions and thus show the tool is trustworthy. Third, we consider concrete specifications of the communication models that are often found in the literature. Thus, the models are classified in terms of ordering properties and according to the level of abstraction of the different specifications. The concept of refinement covers these two aspects. Thus, we model asynchronous point-to-point communication along several levels of refinement and then, with the Event-B method, we establish and prove all the refinements between the communication models and the alternative specifications of each given model. This work results in a detailed map one can use to develop a new model or find the one that best fits given needs. Eventually we explore ways to extend our work to multicast communication that consists in sending messages to several recipients at once. In particular, we highlight the differences in the hierarchy of the models and how we modify our verification tool to handle this communication paradigm.

[pt] A combinação de computação móvel sem fio e tecnologias para a localização de dispositivos possibilitou o surgimento de um novo paradigma de computação conhecido como Serviços Baseados em Localização, cujo objetivo é estudar como prover ao usuário serviços personalizados que dependem da localidade onde este se encontra. Dentre esses serviços, destacam-se aqueles cuja principal função é dar apoio a diferentes formas de comunicação entre usuários de dispositivos móveis. Apesar de vários serviços terem sido desenvolvidos com esse intuito, são poucos os trabalhos que fizeram um levantamento de suas características comuns com o objetivo de projetar uma infra- estrutura genérica que sirva de base para o desenvolvimento de novos serviços. Isso serviu de motivação para esta dissertação, que trata do desenvolvimento de um framework que facilite a construção de serviços para comunicação baseada na localização de usuários móveis. Como estudos de caso, foram instanciados um aplicativo chamado Nita (Notes In The Air), que provê comunicação síncrona e assíncrona entre usuários presentes numa mesma localidade, e um aplicativo para comunicação instantânea similar ao BuddySpace. / [en] The combination of mobile wireless computing and location technology enabled the emergence of a new computing paradigm known as Location-Based Services, whose goal is to study how to provide personalized services to users depending on the their location. Among these services, very useful are the ones which support different kinds of communication between mobile users. Although several services have been developed with this goal, only few work aimed at identifying the common characteristics of these systems, with the goal of designing a generic infrastructure that serves as the basis for the development of new services. This was the main motivation for this thesis work, in which we designed an object framework facilitating the construction of applications for location-based communication among mobile users. As main case studies, we instantiated an application called Nita (Notes In The Air), which provides both synchronous and asynchronous communication between co- located users, and a location-enhanced instant messaging application similar to BuddySpace.

With the advent of Smart Cities, Intelligent Transport System (ITS) has become an efficient way of offering an accessible, safe, and sustainable transportation system. Utilizing advances in Information and Communication Technology (ICT), ITS can maximize the capacity of existing transportation system without building new infrastructure. However, in spite of these technical feasibilities and significant performance-cost ratios, the deployment of ITS is limited in the real world because of several challenges associated with its architectural design. This thesis studies how to design a highly flexible and deployable architecture for ITS, which can utilize the recent technologies such as - cloud computing and the publish/subscribe communication model. In particular, our aim is to offer an ITS infrastructure which provides the opportunity for transport authorities to allocate on-demand computing resources through virtualization technology, and supports a wide range of ITS applications. We propose to use an Infrastructure as a Service (IaaS) model to host large-scale ITS applications for transport authorities in the cloud, which reduces infrastructure cost, improves management flexibility and also ensures better resource utilization. Moreover, we use a publish/subscribe system as a building block for developing a low latency ITS application, which is a promising technology for designing scalable and distributed applications within the ITS domain. Although cloud-based architectures provide the flexibility of adding, removing or moving ITS services within the underlying physical infrastructure, it may be difficult to provide the required quality of service (QoS) which decrease application productivity and customer satisfaction, leading to revenue losses. Therefore, we investigate the impact of service mobility on related QoS in the cloud-based infrastructure. We investigate different strategies to improve performance of a low latency ITS application during service mobility such as utilizing multiple paths to spread network traffic, or deploying recent queue management schemes. Evaluation results from a private cloud testbed using OpenStack show that our proposed architecture is suitable for hosting ITS applications which have stringent performance requirements in terms of scalability, QoS and latency. / Baksidestext: Intelligent Transport System (ITS) can utilize advances in Information and Communication Technology (ICT) and maximize the capacity of existing transportation systems without building new infrastructure. However, in spite of these technical feasibilities and significant performance-cost ratios, the deployment of ITS is limited in the real world because of several challenges associated with its architectural design.  This thesis studies how to design an efficient deployable architecture for ITS, which can utilize the advantages of cloud computing and the publish/subscribe communication model. In particular, our aim is to offer an ITS infrastructure which provides the opportunity for transport authorities to allocate on-demand computing resources through virtualization technology, and supports a wide range of ITS applications. We propose to use an Infrastructure as a Service (IaaS) model to host large-scale ITS applications, and to use a publish/subscribe system as a building block for developing a low latency ITS application. We investigate different strategies to improve performance of an ITS application during service mobility such as utilizing multiple paths to spread network traffic, or deploying recent queue management schemes. / <p>Artikel 4 Network Centric Performance Improvement for Live VM Migration finns i avhandlingen som manuskript. Nu publicerat konferenspaper. </p>

Web-based simulation (WBS) systems offer tradeoffs between user interactivity and hardware requirements striking to seek a balance between the differing concerns. Server-based systems offer little interactivity or concurrent visualization capabilities, while client-based systems have increased hardware requirements asking the user to provide high-end workstations. Concurrent visualization of simulation output proves execution intensive, or unusable in some situations. Creating an execution efficient and user friendly WBS system greatly improves user experience while gaining all of the benefits inherent in a web-based system such as high accessibility and ease of maintenance. In order to provide a usable concurrent visualization WBS this thesis developed the Web-Based Queuing System Simulation System (WebQS3). WebQS3 splits the responsibilities of simulation execution and simulation visualization into a client-server environment; the client is responsible for the visualization display and server is responsible for simulation execution. The system differs from many previous WBS systems in that the client-side application is developed using web-standard technologies such as HTTP, XML, SVG, and ECMAScript instead relying on Java Applets and associated technologies. Using web-standards as the foundation of the client agent opens the visualization and model construction functionality to any user that accesses the application using a web browser while also making the application more scalable in terms of user load. Implementing the client with web-standards also included the development of an asynchronous client-server communication protocol as opposed to traditional synchronous communication protocols used by Java WBS systems. The asynchronous protocol demonstrates similar or better execution performance than similar synchronous communication protocols in most quality characteristics. By creating a WBS system using web-standards implemented in most modern web browsers any user may visit the WebQS3 site and have simulation tools available for use. Providing simulation services on the web makes eases the creation of simulation models my making the tools to readily available while facilitating information sharing and collaboration over the web. The WebQS3 system serves as a model to drive research in WBS systems away from proprietary Java technologies to web standards for front-end visualization technologies. / Master of Science

This dissertation describes research which investigated the use of communication tools in a WebCT learning environment. The instrumental case study investigated the level and frequency of use of the web-based communication tools during a full-fledged course delivery at a university that enrols only full-time students. The unit of analysis was the case and the instruments included group interviews, observation anecdotal notes, communication diaries, focus group and a journal/logbook. A mixed qualitative and quantitative research method was used in this research. The study evaluated how the interactivity and not how either the lesson or the WebCT function. The conceptual framework focused on interactivity, features of communication tools that promote interactivity, as well as the domains such as cognition, motivation and learner interface as aspects that influence the use of communication tools. Various web-based tools were used by a sample consisting of a selected small group of IT students who participated in the study. Those communication tools were used to facilitate learning in WebCT. The results showed a total of 145 interactions for the duration of ten sessions. The WebCT communication tools supported either synchronous or asynchronous communication. Communication tools were used to retrieve information and send text-based messages to lecturers and students. Interaction at different levels was evident between student and student, student and lecturer, lecturer and student, lecturer and lecturer, as well as, student and content. In addition to the WebCT communication tools, students used extra web-based communication tools, to facilitate their learning. It was concluded that with continuous advances in information and communication technology and with ever increasing student numbers at resident universities, more tertiary institutions should offer on-line courses. More communication tools should be considered on WebCT to facilitate more interactive learning. / Dissertation (MEd (Curriculum Studies))--University of Pretoria, 2007. / Curriculum Studies / unrestricted