A Constraint-based Approach for Generating Transformation Patterns

Undoing operations is an indispensable feature for many collaborative applications, mainly collaborative editors. It provides the ability to restore a correct state of shared data after erroneous operations. In particular, selective undo allows to undo any operation and is based on rearranging operations in the history thanks to the Operational Transformation (OT) approach. OT is an optimistic replication technique allowing for updating the shared data concurrently while maintaining convergence. It is a challenging task how to meaningfully combine OT and undo approaches. Indeed, undoing operations that are received and executed out-of-order at different sites leads to divergence cases. Even though various undo solutions have been proposed over the recent years, they are either limited or erroneous. In this paper, we propose a constraint-based approach to address the undo problem. We use Constraint Satisfaction Problem (CSP) theory to devise correct and undoable transformation patterns (w.r.t OT and undo properties) which considerably simplifies the design of collaborative objects.Comment: In Proceedings FOCLASA 2015, arXiv:1512.0694

The process of conserving biodiversity: From planning to evaluating conservation actions on private land in the Cape Lowlands, South Africa

Conservation can be conceptualised as a process of linked phases that contribute to bringing about effective biodiversity protection: (i) a conservation assessment that identifies spatially explicit conservation priorities to provide strategic guidance on where best to invest conservation resources; (ii) a planning phase that takes the spatial priorities forward into implementation processes by setting out a strategy and schedule for undertaking conservation action; (iii) an implementation phase during which conservation interventions are executed; and (iv) an evaluation phase to investigate whether conservation has been successful. In practice, conservation is rarely conducted in this way. The interrelated phases are often undertaken separately, links are neglected, and conservation science to date has focused primarily on the conservation assessment. This has led to the development of highly sophisticated principles and techniques for locating priority conservation areas, but planning and evaluation have received limited research attention: few published studies demonstrate collaborative planning processes that assist with putting conservation assessments into practice, or show on-theground conservation success linked to effective conservation planning and implementation processes. My PhD research aimed to address these knowledge gaps by conducting a conservation assessment and collaborative planning phase that would lead to effective conservation action as determined by an evaluation. The study area was in the critically endangered Cape Lowlands, a conservation priority area in the Cape Floristic Region, South Africa. The highly transformed agricultural production landscape is mostly privately owned; formal biodiversity protection is low; and remnants of natural vegetation (< 9% is left) harbour an exceptionally diverse flora. Strategic conservation interventions coordinated across the Cape Floristic Region (CFR) provided the overall implementation context in the Cape Lowlands. My research was conducted in this real-world practical situation and addresses the whole conservation process, from assessment to evaluation of conservation actions. I first developed a conservation assessment guided by three key questions: âWhat are feasible, efficient, defensible and efficacious solutions for (i) deriving a surrogate layer that represents biodiversity in a region which is characterised by exceptional plant species richness and endemism ; and (ii) considering the connectivity of natural areas in an ecosystem that is highly transformed, fragmented and largely unprotected?â; and âHow can a selection method be developed for identifying and prioritising key biodiversity areas in a landscape identified as 100% irreplaceable?â To answer these questions I identified feasible, efficient, defensible methods focusing on three key aspects: (i) producing a biodiversity surrogate map of original vegetation cover using two alternative approaches: simple expert mapping and statistical modelling integrating plant species and environmental data; (ii) designing selection units based on vegetation connectivity in a simple technique to include spatial attributes of conservation areas before identifying key biodiversity areas; (iii) developing a prioritisation method based on a simple scoring system and verifying results with MARXAN-selected priority areas. In all vi three cases I found that the simple conservation assessment methods produced suitable outputs for further integration in the assessment and in decision-making during planning. (i) The expert map was as effective as the vegetation model and required fewer resources to be produced since the model relied on resource-intensive species data collection. (ii) In comparison with commonly used cadastre-based units, connectivity-based selection units captured connected vegetation more effectively and area-efficiently in units that served as the basis for priority area selection. (iii) Scoring provided a feasible, defensible mechanism for prioritising key biodiversity areas in the Cape Lowlands where all remaining vegetation has been identified as 100% irreplaceable. The planning phase complemented the assessment. Key guiding questions here were âHow can collaborative planning be used to translate the conservation assessmentâs technical outputs into timebased conservation goals and into useful products for implementation?â and âWhat constitutes effective planning in the conservation process? Through a collaborative scheduling process, I developed timebased conservation goals for action in the Cape Lowlands. This was undertaken in two work sessions with scientists, planners and conservation practitioners from the implementing agency, CapeNature. Scheduling was guided by (i) scoring-derived biodiversity-driven spatial priorities that made intuitive sense to implementers; and (ii) conservation opportunities and constraints (including resources) identified by the practitioners. Scheduling was conducted with reference to the on-going development of a private land conservation strategy for the CFR to be piloted in the Cape Lowlands. The scheduling process was an effective platform for taking spatial priorities from the assessment towards implementation: the discourse-based collaborative planning was constructive and led to consensusbased final products, including a 20-year and 5-year conservation plan setting out spatially explicit goals for conservation interventions in the Cape Lowlands. The main limitation of the process was that resource planning was not integrated explicitly enough to identify realistic goals. This highlighted the importance of integrating detailed resource considerations in future planning. Finally, to address the question âTo what extent has the Cape Lowlands conservation plan been implemented after five years of off-reserve conservation interventions in the region?â I developed a protocol for evaluating the effectiveness of conservation action in the Cape Lowlands. I assessed (i) the extent to which the goals conservation plans produced in the planning phase had been implemented; and (ii) the achievements of incentive-based conservation stewardship interventions on private land in the Cape Lowlands and CFR. Achievements were measured as hectares of vegetation protected through voluntary and legally-binding contractual conservation agreements between landowners and conservation organisations. The evaluation revealed that (i) CapeNatureâs stewardship interventions in the Cape Lowlands focused on priority areas identified in the 5- and 20-year conservation plans, thus demonstrating effective execution of the plans; (ii) private land conservation interventions have been remarkably successful and cost-effective: 68604ha priority vegetation were protected in the CFR under conservation agreements by end 2007, rivalling private land biodiversity conservation in the U.S.A. and Latin America, and more than 8000ha in the critically endangered Cape Lowlands at a cost of R 6.8 vii Million (< 1 million US$). The evaluation identified the long-term financial sustainability of current implementation programmes as the most significant threat to future success in private land conservation interventions in the Cape Lowlands and CFR. There is significant scope to design future monitoring and evaluation systems to measure ecological gains due to specific conservation actions, not done in the Cape Lowlands study, and to tailor approaches to suit specific programme stages. This PhD provides a rare overview of an entire conservation cycle with linked phases that has led to biodiversity protection. The study highlights that an effective long-term process demands significant investment in (i) a diverse (growing) set of skills and expertise to solve complex conservation situations; (ii) time, especially for visible implementation success; and (iii) well-allocated resources (money, time, skills, research attention) across all phases in the conservation process. This is necessary as each phase is needed to achieve the ultimate conservation goal: I show in the Cape Lowlands that a simple conservation assessment with limited funds (R1.8 million over 3 years) can be highly effective in guiding action towards priority areas. Important here is to develop rapid, defensible methods for cost-effective assessments and linking these with in-depth planning processes. Planning and evaluation in the Cape Lowlands were essential connecting phases that continue to support implementation success. In the context of on-going conservation action, planning and evaluation need to become part of a cyclical conservation process geared towards improved practices. I suggest that significantly greater investment in planning and evaluation research is essential to move conservation science forward in fulfilling its fundamental goal of strategically guiding where, when and how to invest optimally in conservation interventions. This will be exceptionally beneficial for undertaking effective conservation interventions and will help to clearly demonstrate the value of the research for conservation practice

Digital ecosystems : a distributed service oriented approach for business transactions

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Extending and Relating Semantic Models of Compensating CSP

Business transactions involve multiple partners coordinating and interacting with each other. These transactions have hierarchies of activities which need to be orchestrated. Usual database approaches (e.g.,checkpoint, rollback) are not applicable to handle faults in a long running transaction due to interaction with multiple partners. The compensation mechanism handles faults that can arise in a long running transaction. Based on the framework of Hoare's CSP process algebra, Butler et al introduced Compensating CSP (cCSP), a language to model long-running transactions. The language introduces a method to declare a transaction as a process and it has constructs for orchestration of compensation. Butler et al also defines a trace semantics for cCSP. In this thesis, the semantic models of compensating CSP are extended by defining an operational semantics, describing how the state of a program changes during its execution. The semantics is encoded into Prolog to animate the specification. The semantic models are further extended to define the synchronisation of processes. The notion of partial behaviour is defined to model the behaviour of deadlock that arises during process synchronisation. A correspondence relationship is then defined between the semantic models and proved by using structural induction. Proving the correspondence means that any of the presentation can be accepted as a primary definition of the meaning of the language and each definition can be used correctly at different times, and for different purposes. The semantic models and their relationships are mechanised by using the theorem prover PVS. The semantic models are embedded in PVS by using Shallow embedding. The relationships between semantic models are proved by mutual structural induction. The mechanisation overcomes the problems in hand proofs and improves the scalability of the approach

Cooperative planning in multi-agent systems

Tesis por compendio[EN] Automated planning is a centralized process in which a single planning entity, or agent, synthesizes a course of action, or plan, that satisfies a desired set of goals from an initial situation. A Multi-Agent System (MAS) is a distributed system where a group of autonomous agents pursue their own goals in a reactive, proactive and social way. Multi-Agent Planning (MAP) is a novel research field that emerges as the integration of automated planning in MAS. Agents are endowed with planning capabilities and their mission is to find a course of action that attains the goals of the MAP task. MAP generalizes the problem of automated planning in domains where several agents plan and act together by combining their knowledge, information and capabilities. In cooperative MAP, agents are assumed to be collaborative and work together towards the joint construction of a competent plan that solves a set of common goals. There exist different methods to address this objective, which vary according to the typology and coordination needs of the MAP task to solve; that is, to which extent agents are able to make their own local plans without affecting the activities of the other agents. The present PhD thesis focuses on the design, development and experimental evaluation of a general-purpose and domain-independent resolution framework that solves cooperative MAP tasks of different typology and complexity. More precisely, our model performs a multi-agent multi-heuristic search over a plan space. Agents make use of an embedded search engine based on forward-chaining Partial Order Planning to successively build refinement plans starting from an initial empty plan while they jointly explore a multi-agent search tree. All the reasoning processes, algorithms and coordination protocols are fully distributed among the planning agents and guarantee the preservation of the agents' private information. The multi-agent search is guided through the alternation of two state-based heuristic functions. These heuristic estimators use the global information on the MAP task instead of the local projections of the task of each agent. The experimental evaluation shows the effectiveness of our multi-heuristic search scheme, obtaining significant results in a wide variety of cooperative MAP tasks adapted from the benchmarks of the International Planning Competition.[ES] La planificación automática es un proceso centralizado en el que una única entidad de planificación, o agente, sintetiza un curso de acción, o plan, que satisface un conjunto deseado de objetivos a partir de una situación inicial. Un Sistema Multi-Agente (SMA) es un sistema distribuido en el que un grupo de agentes autónomos persiguen sus propias metas de forma reactiva, proactiva y social. La Planificación Multi-Agente (PMA) es un nuevo campo de investigación que surge de la integración de planificación automática en SMA. Los agentes disponen de capacidades de planificación y su propósito consiste en generar un curso de acción que alcance los objetivos de la tarea de PMA. La PMA generaliza el problema de planificación automática en dominios en los que diversos agentes planifican y actúan conjuntamente mediante la combinación de sus conocimientos, información y capacidades. En PMA cooperativa, se asume que los agentes son colaborativos y trabajan conjuntamente para la construcción de un plan competente que resuelva una serie de objetivos comunes. Existen distintos métodos para alcanzar este objetivo que varían de acuerdo a la tipología y las necesidades de coordinación de la tarea de PMA a resolver; esto es, hasta qué punto los agentes pueden generar sus propios planes locales sin afectar a las actividades de otros agentes. La presente tesis doctoral se centra en el diseño, desarrollo y evaluación experimental de una herramienta independiente del dominio y de propósito general para la resolución de tareas de PMA cooperativa de distinta tipología y nivel de complejidad. Particularmente, nuestro modelo realiza una búsqueda multi-agente y multi-heurística sobre el espacio de planes. Los agentes hacen uso de un motor de búsqueda embebido basado en Planificación de Orden Parcial de encadenamiento progresivo para generar planes refinamiento de forma sucesiva mientras exploran conjuntamente el árbol de búsqueda multiagente. Todos los procesos de razonamiento, algoritmos y protocolos de coordinación están totalmente distribuidos entre los agentes y garantizan la preservación de la información privada de los agentes. La búsqueda multi-agente se guía mediante la alternancia de dos funciones heurísticas basadas en estados. Estos estimadores heurísticos utilizan la información global de la tarea de PMA en lugar de las proyecciones locales de la tarea de cada agente. La evaluación experimental muestra la efectividad de nuestro esquema de búsqueda multi-heurístico, que obtiene resultados significativos en una amplia variedad de tareas de PMA cooperativa adaptadas a partir de los bancos de pruebas de las Competición Internacional de Planificación.[CA] La planificació automàtica és un procés centralitzat en el que una única entitat de planificació, o agent, sintetitza un curs d'acció, o pla, que satisfau un conjunt desitjat d'objectius a partir d'una situació inicial. Un Sistema Multi-Agent (SMA) és un sistema distribuït en el que un grup d'agents autònoms persegueixen les seues pròpies metes de forma reactiva, proactiva i social. La Planificació Multi-Agent (PMA) és un nou camp d'investigació que sorgeix de la integració de planificació automàtica en SMA. Els agents estan dotats de capacitats de planificació i el seu propòsit consisteix en generar un curs d'acció que aconseguisca els objectius de la tasca de PMA. La PMA generalitza el problema de planificació automàtica en dominis en què diversos agents planifiquen i actúen conjuntament mitjançant la combinació dels seus coneixements, informació i capacitats. En PMA cooperativa, s'assumeix que els agents són col·laboratius i treballen conjuntament per la construcció d'un pla competent que ressolga una sèrie d'objectius comuns. Existeixen diferents mètodes per assolir aquest objectiu que varien d'acord a la tipologia i les necessitats de coordinació de la tasca de PMA a ressoldre; és a dir, fins a quin punt els agents poden generar els seus propis plans locals sense afectar a les activitats d'altres agents. La present tesi doctoral es centra en el disseny, desenvolupament i avaluació experimental d'una ferramenta independent del domini i de propòsit general per la resolució de tasques de PMA cooperativa de diferent tipologia i nivell de complexitat. Particularment, el nostre model realitza una cerca multi-agent i multi-heuristica sobre l'espai de plans. Els agents fan ús d'un motor de cerca embegut en base a Planificació d'Ordre Parcial d'encadenament progressiu per generar plans de refinament de forma successiva mentre exploren conjuntament l'arbre de cerca multiagent. Tots els processos de raonament, algoritmes i protocols de coordinació estan totalment distribuïts entre els agents i garanteixen la preservació de la informació privada dels agents. La cerca multi-agent es guia mitjançant l'aternança de dues funcions heurístiques basades en estats. Aquests estimadors heurístics utilitzen la informació global de la tasca de PMA en lloc de les projeccions locals de la tasca de cada agent. L'avaluació experimental mostra l'efectivitat del nostre esquema de cerca multi-heurístic, que obté resultats significatius en una ampla varietat de tasques de PMA cooperativa adaptades a partir dels bancs de proves de la Competició Internacional de Planificació.Torreño Lerma, A. (2016). Cooperative planning in multi-agent systems [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/65815TESISPremiadoCompendi

Rational Cybersecurity for Business

Use the guidance in this comprehensive field guide to gain the support of your top executives for aligning a rational cybersecurity plan with your business. You will learn how to improve working relationships with stakeholders in complex digital businesses, IT, and development environments. You will know how to prioritize your security program, and motivate and retain your team. Misalignment between security and your business can start at the top at the C-suite or happen at the line of business, IT, development, or user level. It has a corrosive effect on any security project it touches. But it does not have to be like this. Author Dan Blum presents valuable lessons learned from interviews with over 70 security and business leaders. You will discover how to successfully solve issues related to: risk management, operational security, privacy protection, hybrid cloud management, security culture and user awareness, and communication challenges. This open access book presents six priority areas to focus on to maximize the effectiveness of your cybersecurity program: risk management, control baseline, security culture, IT rationalization, access control, and cyber-resilience. Common challenges and good practices are provided for businesses of different types and sizes. And more than 50 specific keys to alignment are included. What You Will Learn Improve your security culture: clarify security-related roles, communicate effectively to businesspeople, and hire, motivate, or retain outstanding security staff by creating a sense of efficacy Develop a consistent accountability model, information risk taxonomy, and risk management framework Adopt a security and risk governance model consistent with your business structure or culture, manage policy, and optimize security budgeting within the larger business unit and CIO organization IT spend Tailor a control baseline to your organization’s maturity level, regulatory requirements, scale, circumstances, and critical assets Help CIOs, Chief Digital Officers, and other executives to develop an IT strategy for curating cloud solutions and reducing shadow IT, building up DevSecOps and Disciplined Agile, and more Balance access control and accountability approaches, leverage modern digital identity standards to improve digital relationships, and provide data governance and privacy-enhancing capabilities Plan for cyber-resilience: work with the SOC, IT, business groups, and external sources to coordinate incident response and to recover from outages and come back stronger Integrate your learnings from this book into a quick-hitting rational cybersecurity success plan Who This Book Is For Chief Information Security Officers (CISOs) and other heads of security, security directors and managers, security architects and project leads, and other team members providing security leadership to your busines

Convergence et sécurité d'accès dans les systèmes d'édition collaborative massivement répartis

RÉSUMÉ Parmi les défis des systèmes d'édition collaborative figure la cohérence des objets partagés. Dans la perspective d'une édition cohérente, le système doit garantir la convergence. Pour assurer la cohérence des objets partagés, la littérature propose plusieurs solutions. Les différentes approches majeures proposées sont : l'approche des types de données commutatives répliquées (CRDT) et l'approche de la transformée opérationnelle (OT). L'approche CRDT considère des opérations commutatives qui peuvent être exécutées dans un ordre différent. L'une des difficultés auxquelles CRDT se bute réside en la commutativité des opérations. Toutes les opérations d'édition doivent être commutatives afin d'être exécutées dans un ordre quelconque. L'approche de la transformée opérationnelle quant à elle propose une transformation des opérations distantes reçues par rapport aux opérations qui lui sont concurrentes ; même si elles sont déjà exécutées. Pour effectuer les transformations, l'approche OT utilise un algorithme de transformation inclusive (IT). Dans la littérature, plusieurs travaux ont prouvé que les principaux algorithmes de transformation inclusive proposés ne satisfont pas le critère de convergence. Outre la cohérence, la sécurisation des interactions est un autre défi des systèmes d'édition collaborative. Le contrôle d'accès est l'un des modèles de politiques de sécurité applicable dans ce cadre. Il s'agit d'autoriser ou d'interdire l'édition à certains utilisateurs. Le contrôle d'accès doit être uniformément déployé pour éviter de compromettre la cohérence des opérations d'édition. Une opération d'édition valide sur un site doit l'être partout. Une opération refusée sur un site doit être refusée partout. Dans le contexte étudié, le protocole de sécurité est fiable s'il préserve la cohérence du système. Fournir cette preuve de fiabilité est une tâche ardue. Le nombre de cas à examiner est infini. De plus, pour une vérification automatique, le défaut de ressources survient si des techniques appropriées ne sont pas exploitées. Dans cette thèse, nous nous intéressons aux défis que constituent la convergence et le contrôle d'accès dans les systèmes d'édition collaborative répartis. Nous considérons un objet textuel à structure linéaire qui est massivement édité dans une architecture répartie. L'approche de gestion de cohérence utilisée est la transformée opérationnelle. Ainsi, chaque utilisateur a sa copie locale du document partagé. Les opérations générées sur un site sont aussitôt diffusées aux autres utilisateurs. Elles peuvent être exécutées dans un ordre quelconque. Les types d'opérations d'édition sont : l'insertion d'un caractère et la suppression de caractère. Nous intégrons également un protocole de contrôle d'accès à l'édition collaborative. Notre thèse se présente sous la forme de trois articles scientifiques, chacun traitant d'une problématique bien spécifique. Dans le premier article, nous abordons la problématique de la convergence. Nous avons adopté une démarche en plusieurs étapes. Une exploration a été initialement faite afin de vérifier s'il est possible d'avoir une fonction IT convergente. En utilisant la méthode de la synthèse de contrôleur et les automates de jeu, nos investigations ont révélé qu'aucune IT basée uniquement sur le caractère et la position ne peut garantir une convergence. L'identification des causes de divergence a permis d'amorcer la résolution du « problème de synthèse de contrôleur ». Ainsi, un troisième paramètre a été ajouté aux opérations d'insertion. Il permet de manipuler le nombre de caractères supprimés avant la position d'insertion indiquée. Une fonction de détermination de la valeur de ce paramètre a été proposée. Une fonction IT a été par la suite proposée, en tenant compte des propositions précédentes. En utilisant la vérification sur modèle (model-checking), la preuve a été apportée que notre IT garantit bien la convergence. Le deuxième article propose l'intégration d'un protocole de sécurité optimiste. L'article aborde la problématique de la fiabilité du protocole dans un espace d'états infini. Il est déployé au dessus de protocole de synchronisation du système d'édition collaborative. Nous faisons l'hypothèse que le système vérifie la propriété de cohérence en l'absence du contrôle d'accès. Pour affronter les difficultés relatives à la preuve de fiabilité, l'approche du model-checking symbolique a été préférée. Le model-checking borné a été utilisé avec l'outil Alloy. L'exploration faite pour des instances dont la taille maximale est de treize « signatures », a permis de conclure la préservation de la cohérence par le protocole de contrôle d'accès. Notons que ces instances ne sont pas massives mais la combinatoire résultante n'est pas négligeable. Le troisième article aborde la problématique de réduction de système. Des investigations ont été menées afin d'avoir un modèle fini équivalent au système d'édition collaborative, au regard de la propriété de cohérence. Le modèle abstrait proposé comporte trois sites coopératifs, dont l'un est administrateur. Ce modèle à espace d'états fini étant prouvé équivalent par rapport à la propriété de cohérence, au système à espace d'états infini, il a servi de cadre pour la vérification automatique. En utilisant l'outil Uppaal et le formalisme d'automate, nous avons prouvé par model-checking que le modèle abstrait préserve la cohérence. Par conséquent, le protocole de contrôle d'accès préserve la cohérence de système d'édition collaborative. Nos travaux comportent quelques limitations liées à leur portée. Nous avons manipulé des objets textuels à structure linéaire sur lesquels ne sont appliquées que des opérations d'insertion et de suppression de caractères. De plus, la gestion des droits d'accès est basée sur un modèle mono-administrateur. La performance du protocole de contrôle d'accès n'a pas non plus été prise en compte. Les travaux auraient sans doute plus d'envergure s'ils couvraient plusieurs types d'objets, plusieurs types d'opérations d'édition, plusieurs administrateurs et une étude de performance. Nos futures travaux pourraient être consacrés à l'élargissement de la portée de la présente thèse.----------ABSTRACT The consistency of the shared documents is one of the most important challenges in collaborative editing systems. To achieve consistency, a solution must ensure the convergence criteria. Several solutions are proposed in litterature to achieve consistency of the shared documents. The major approaches are: commutative replicated data type (CRDT) and operational transformation (OT). CRDT considers some commutative operations which could be executed in different order. The main difficulty of CRDT is to compute commutative operations. OT approach proposes to transform remote operations against their concurrent operations, even if they are already executed. An inclusive transformation function is used to compute the transformations. In the litterature, several works show that the main inclusive transformation (IT) functions proposed do not ensure convergence. Besides consistency, security of the edition is another challenge in distributed collaborative systems. Access control is a model of security policy that could be used. It consists of granting or revoking editing authorizations for users. Access control must be uniformly deployed to not compromise the consistency of the system. A valid editing operation at one site must be valid at all other sites. As the same time, an invalid operation at one site, must be invalid everywhere. In the current context, the security protocol is reliable if it preserves the consistency of the system. Produce the proof of reliability is difficult. It requires examining infinite number of cases. In addition, with automatic verification, ressources become insufficient if appropriate techniques are not used. This thesis is interested in consistency and access control challenges in distributed collaborative editing systems. It considers a textual object with a linear structure that is massively edited in a distributed architecture. OT is used to manage consistency. Each user has a local copy of the shared document. Locally-generated operations are immediately broadcast to other users. Operations could be executed in any order. Their types are inserting and deleting characters. To ensure security, collaborative edition is combined with an access control protocol. The thesis consists of three scientific articles. Each of them deals with a specific problem. In the first article, we adress the problem of consistency and proceed in several steps. Initially, we explore the existence of convergent IT functions of OT, which ensure data consistency. Using the controller synthesis approach and game automata, we conclude that there is no IT function, based only on character and position as parameters of insert and delete operations, which ensure data consistency. The investigation of the causes of divergence led to solve the controller synthesis problem. Thus, a new parameter is added to the insert operation signature. It handles the number of characters deleted before the inserting position. The function needed to compute the value of this parameter is provided. Finally, based on these contributions, we propose an IT function and show that it ensures convergence. The proof is achieved by a symbolic model-checking emulated using the tool Uppaal. The second article adresses the reliability of security protocol in an infinite state space. An optimist access control protocol is considered to be deployed over any correct synchronization protocol. The symbolic model-checking approach is choosen to deal with the proof of reliabi--lity. For this purpose, bounded model-checking is used with the tool Alloy. Exploration made with instances whose maximum size is thirteen allow to conclude the preservation of consistency by the access control protocol. These instances are not massive but the resulting combinatorial is important. The third article adresses the problem of system reduction. In this article, we investigate a finite model equivalent to a distributed collaborative editing system, with regard to consistency. The abstract model proposed consists of three cooperative sites including the administrator. This finite state model is proved by model-checking to preserve consistency. Consequently, the access control protocol preserves consistency of any correct distributed collaborative editing system. The model-checking techniques exploits Uppaal tool and automata. Our work has several limitations. We consider textual objects with linear structure. These objects are edited by applying some operations which are inserting and deleting characters. In addition, the management of access rights is based on one-administrator model. The performance study of the access control protocol is not done. The work would probably be more extensive if it covered several types of objects, several types of editing operations, many administrators and the performance study. Our future work could be devoted to the widening of the scope of this thesis

A speculative execution approach to provide semantically aware contention management for concurrent systems

PhD ThesisMost modern platforms offer ample potention for parallel execution of concurrent programs yet concurrency control is required to exploit parallelism while maintaining program correctness. Pessimistic con- currency control featuring blocking synchronization and mutual ex- clusion, has given way to transactional memory, which allows the composition of concurrent code in a manner more intuitive for the application programmer. An important component in any transactional memory technique however is the policy for resolving conflicts on shared data, commonly referred to as the contention management policy. In this thesis, a Universal Construction is described which provides contention management for software transactional memory. The technique differs from existing approaches given that multiple execution paths are explored speculatively and in parallel. In the resolution of conflicts by state space exploration, we demonstrate that both concur- rent conflicts and semantic conflicts can be solved, promoting multi- threaded program progression. We de ne a model of computation called Many Systems, which defines the execution of concurrent threads as a state space management problem. An implementation is then presented based on concepts from the model, and we extend the implementation to incorporate nested transactions. Results are provided which compare the performance of our approach with an established contention management policy, under varying degrees of concurrent and semantic conflicts. Finally, we provide performance results from a number of search strategies, when nested transactions are introduced