Data optimizations for constraint automata

Constraint automata (CA) constitute a coordination model based on finite automata on infinite words. Originally introduced for modeling of coordinators, an interesting new application of CAs is implementing coordinators (i.e., compiling CAs into executable code). Such an approach guarantees correctness-by-construction and can even yield code that outperforms hand-crafted code. The extent to which these two potential advantages materialize depends on the smartness of CA-compilers and the existence of proofs of their correctness. Every transition in a CA is labeled by a "data constraint" that specifies an atomic data-flow between coordinated processes as a first-order formula. At run-time, compiler-generated code must handle data constraints as efficiently as possible. In this paper, we present, and prove the correctness of two optimization techniques for CA-compilers related to handling of data constraints: a reduction to eliminate redundant variables and a translation from (declarative) data constraints to (imperative) data commands expressed in a small sequential language. Through experiments, we show that these optimization techniques can have a positive impact on performance of generated executable code

Towards more efficient solution of conditional constraint satisfaction problems

The focus of the thesis is on improving solving constraint satisfaction problems (CSPs) that change with certain conditions. This special class of problems, which we call conditional CSPs, has proved very useful in modeling important applications, such product configuration and design, and distributed software diagnosis and network management. The problem conditions model choices customers make to configure a product, or they are installation settings or actual observations of a running system that is monitored for diagnosis purpose. The key, novel contribution of this thesis are two approaches for improving solving methods and the use of random conditional CSPs to evaluate the performance of these methods. With the first approach we propose new algorithms for solving conditional CSPs. These algorithms propagate problem constraints and conditions. The second approach explores the feasibility of reformulating the problem into a standard CSP and introduces new reformulation algorithms. The implementation results have been evaluated experimentally. The experimental design has extensive test suites of randomly generated standard and conditional CSPs for which general problem parameters, such as density and satisfiability, were varied, as well as specialized parameters that characterize the representation of problem conditions. The significance of the work lies in the advance of problem resolution for the class of conditional CSPs and the experimental analysis for the proposed new algorithms. The limited solving developments known in the literature of the class of conditional CSPs, a backtrack search algorithm tested on a handful of small problem examples, have been taken an important step further and aligned with efforts reported for standard and other special classes of CSPs

Automatic design of the gravity-reducing propulsion system of the TALARIS Hopper Testbed

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, September 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 87-93).This thesis describes a Systems Engineering tool for automatic design, presents the results of its application to the problem of designing Earth-based reduced-gravity simulators, and compares the performance of the found optimal design solutions with that of the MIT TALARIS Hopper Testbed. Earth-based reduced-gravity simulators are platforms that allow hosted vehicles to experience a dynamic environment -from a guidance, navigation, and control perspective- analog to other planetary surfaces. Simulators are used for system development and operator training purposes. Specifically, reduced-gravity simulators produce a constant vertical thrust equal to a fraction of the weight of the studied vehicle, this yielding a perceived gravity equal to the gravity of the celestial body of interest. Planetary hoppers explore planetary surfaces through hopping, i.e. low altitude and short-duration flying. Recently, these systems have gained popularity as cost-effective means for planetary exploration due to their larger operational flexibility compared to other exploration systems. The tool developed as part of this thesis eases the compilation and use of parts catalogs in the design task, includes real-time visualization of the search process, supports the output of multiple solutions that optimize conflicting goals, efficiently calculates Pareto frontiers of solutions, and can integrate external solvers and simulators seamlessly. Chapter 1 overviews the engineering challenges associated with Earth-based reduced-gravity simulators applied to planetary hoppers. Chapter 2 provides the context knowledge required for the development of the individual tasks in this thesis. Chapter 3 discusses the engineering literature covering relevant previous work. Chapter 4 describes the selected approach and the tool that has been developed for the design of the propulsion system of the simulator. Chapter 5 discusses the applicability of the approach and design tool to the case of the MIT TALARIS Hopper Testbed. Chapter 6 summarizes the results and outlines avenues for future research in this field.by Jorge Cañizales Díaz.S.M

Contribution à l'élaboration d'un formalisme gérant la pertinence pour les problèmes d'aide à la conception à base de contraintes

Les travaux présentés dans cette thèse portent sur l'aide à la conception et à la configuration. Une intégration de différents concepts existant dans les domaines de la programmation par contraintes a été réalisée. Cette intégration a pu être testée sur une implémentation basée sur des arbres syntaxiques représentant un CSP (problème de satisfaction de contraintes) modélisant un problème de conception ou configuration. La première partie de la thèse présente les domaines de la conception et de la configuration, et en fait ressortir les besoins pour l'aide à la décision : paramètres discrets et continus, organisation hiérarchique et éléments optionnels. Différentes approches à base de contraintes permettant de répondre à ces besoins sont ensuite détaillées. La seconde partie présente les RCSP (CSP gérant la pertinence), qui intègrent les différents mécanismes vus dans la première partie. Des préconisations de modélisation pour les problèmes de conception et de configuration sont établies. L'outil réalisé est ensuite présenté, dans un premier temps pour le traitement de problèmes CSP et dans un deuxième temps pour le traitement de RCSP

Contribution à l'élaboration d'un formalisme gérant la pertinence pour les problèmes d'aide à la conception à base de contraintes

Les travaux présentés dans cette thèse portent sur l'aide à la conception et à la configuration. Une intégration de différents concepts existant dans les domaines de la programmation par contraintes a été réalisée. Cette intégration a pu être testée sur une implémentation basée sur des arbres syntaxiques représentant un CSP (problème de satisfaction de contraintes) modélisant un problème de conception ou configuration. La première partie de la thèse présente les domaines de la conception et de la configuration, et en fait ressortir les besoins pour l'aide à la décision : paramètres discrets et continus, organisation hiérarchique et éléments optionnels. Différentes approches à base de contraintes permettant de répondre à ces besoins sont ensuite détaillées. La seconde partie présente les RCSP (CSP gérant la pertinence), qui intègrent les différents mécanismes vus dans la première partie. Des préconisations de modélisation pour les problèmes de conception et de configuration sont établies. L'outil réalisé est ensuite présenté, dans un premier temps pour le traitement de problèmes CSP et dans un deuxième temps pour le traitement de RCSP. ABSTRACT : The research work presented in this thesis deals with assistance to design and configuration tasks. An integration of different existing concepts of constraint programming has been achieved. This integration has been tested on an implementation based upon syntaxic trees. The syntaxic trees allow to express different kinds of CSP (Constraint Satisfaction Problem) which model design or configuration problems. The first part presents the fields of design and configuration, and aims at identifying the needs for decision aid: different kinds of parameters (discrete and continuous), hierarchical organisation and optionnal elements. Different constraint-based approaches which may fulfill any need are then detailed. The second part presents the RCSP (Relevancy CSP), which are an integration of different CSP from the literature seen in the first part. Some recommendations for modeling design or configuration problems are set up. The implementation is then presented, on the one hand for CSP processing and on the other hand for RCSP processing