Experimenting a Conflict-Driven Clause Learning Algorithm

International audienceExperimentation of new algorithms is the usual companion section of papers dealing with SAT. However, the behavior of those algorithms is so unpredictable that even strong experiments (hundreds of benchmarks, dozen of solvers) can be still misleading. We present here a set of experiments of very small changes of a canonical Conflict Driven Clause Learning (CDCL) solver and show that even very close versions can lead to very different behaviors. In some cases, the best of them could perfectly have been used to convince the reader of the efficiency of a new method for SAT. This observation can be explained by the lack of real experimental studies of CDCL solvers

Efficient Web Requests Scheduling Considering Resources Sharing

International audienceRequests scheduling in Web servers is a hot research topic. Many works aim at providing optimal algorithms according to various metrics. Most of these works are based on classical scheduling metrics, considering jobs completion times, but ignoring intermediate states. We claim that this choice conduces to the design of algorithm that do not efficiently share the system resources. Indeed, Web servers have some properties that make them different than the system considered in usual scheduling theory. The classical round-robin policy, used in most production Web servers, has intrinsic qualities: it shares equally the system resources and avoids any job starvation. We introduce a novel parameterizable algorithm proposing a compromise between the benefits of the round-robin and the policies that provide the best performances. Then, we discuss the appropriate choice of the parameter depending in the requirements and the context of the Web server

L’irrédentisme des valeurs dans le droit : la quête du fondement axiologique

Le droit possède une texture ouverte et téléologique. Il se présente comme un outil indispensable pour « consolider les choix de valeurs en permettant de les formaliser et de les mettre en oeuvre. Derrière le miroir du droit, se trouve, sous-jacents, les valeurs et les principes. Parfois confondues, ces deux notions sont intrinsèques à la notion même de droit, et servent de soubassement à la formulation de décisions judiciaires. On peut dire de ces notions qu’elles sont irrédentes, c’est-à-dire que, comme dans l’imaginaire politique italien du début du 20e siècle, les principes et les valeurs ne peuvent être séparés du corpus juridique, tout comme les terres irrédentes ne pouvaient être séparées de l’identité italienne.Abstract: Law possesses an open and teleological angle as it presents itself as an indispensible tool to consolidate the choice of values by formalizing them as well as putting them to use. Underlying behind the mirror of law, one finds values and principles. These two notions are intrinsic to the concept of law and therefore serve as the foundation of legal decisionmaking. One can say that these notions are irredentes, in other words, similar to the early 20th Century Italian political imagery, the principles and values cannot be separated from the judicial body, much like the irredente lands could not be separated from the Italian identity

LINEAR APPROXIMATION OF OPEN-CHANNEL FLOW ROUTING WITH BACKWATER EFFECT

International audienceThis paper proposes a new model for linear flow routing in open-channels. The proposed model, called LBLR for Linear Backwater Lag and Route, is a first order with delay model that explicitly takes into account two parameters which are usually neglected: 1) the downstream boundary condition and 2) the nonuniform flow conditions, both of which are shown to have a strong influence on the flow dynamics. The model parameters are obtained analytically from the pool characteristics (geometry, friction, discharge and downstream boundary condition). A frequency domain approach is used to compute the frequency response of the linearized Saint-Venant equations. This model is then approximated by a first order plus delay model using the moment matching method. The proposed model is shown to perform better than existing models when the flow is affected by backwater and/or by different downstream boundary conditions from the one corresponding to uniform flow

Cross-layer enhancement of Web servers dedicated to small devices

De nos jours, les systèmes embarqués sont de plus en plus nombreux et ont un besoin grandissant d'accessibilité. Au lieu d'utiliser des protocoles dédiés, imposant l'utilisation de logiciels clients et serveurs, nous soutenons que l'utilisation de serveurs Web sur ces cibles en augmente l'accessibilité ainsi que la maintenabilité et facilite le développement. Ainsi, tout le monde peut accéder et configurer un routeur, un capteur de terrain ou un système domotique depuis n'importe quel ordinateur ou PDA, via un simple navigateur Web. En utilisant les technologies modernes du Web telles qu'AJAX, des applications interactives peuvent être servies. Cependant, cette solution est techniquement difficile à mettre en oeuvre à cause des limitations matérielles des systèmes embarqués ciblés (souvent un CPU à quelques MHz et seulement quelques kilo-octets de RAM), comparées à la lourdeur des serveurs Web classiques (et des protocoles du Web). Dans ce rapport, nous présentons tout d'abord une analyse transversale des protocoles TCP/IP lorsqu'utilisés pour servir des applications Web dynamiques. Nous testons des serveurs Web embarqués existants et analysons leurs performances. A partir de cette analyse, nous proposons de nouvelles solutions pour concevoir des serveurs Web efficaces et peu consommateurs de mémoire. Nous avons implémenté toutes nos propositions, engendrant un nouveau serveur Web embarqué, capable de servir efficacement des applications Web dynamiques avec une consommation en RAM de moins d'un kilo-octet, sans aucun système sous-jacent

The Web of Things: interconnecting devices with high usability and performance

International audienceIn this paper, we show that Web protocols and technologies are good candidates to design the Internet of Things. This approach allows anyone to access embedded devices through a Web application, via a standard Web browser. This Web of Things requires to embed Web servers in hardware-constrained devices. We first analyze the traffics embedded Web servers have to handle. Starting from this analysis, we propose a new way to design embedded Web servers, using a dedicated TCP/IP stack and numerous cross-layer off-line pre-calculation (where information are shared between IP, TCP, HTTP and the Web application). We finally present a prototype -- named Smews -- as a proof of concept of our proposals. It has been embedded in tiny devices (smart cards, sensors and other embedded devices), with a requirement of only 200 bytes of RAM and 7 kilo-bytes of code. We show that it is significantly faster than other state of the art solutions. We made Smews source code publically available under an open-source license

Serving Embedded Content via Web Applications: Model, Design and Experimentation

International audienceEmbedded systems such as smart cards or sensors are now widespread, but are often closed systems, only accessed via dedicated terminals. A new trend consists in embedding Web servers in small devices, making both access and application development easier. In this paper, we propose a TCP performance model in the context of embedded Web servers, and we introduce a taxonomy of the contents possibly served by Web applications. The main idea of this paper is to adapt the communication stack behavior to application contents properties. We propose a strategies set fitting with each type of content. The model allows to evaluate the benefits of our strategies in terms of time and memory charge. By implementing a real use case on a smart card, we measure the benefits of our proposals and validate our model. Our prototype, called Smews, makes a gap with state of the art solutions both in terms of performance and memory charge