Yet Another Implementation of Attribute Evaluation

We introduce another item in the already large list of techniques for attribute evaluation. Our algorithm consists in computing attributes by reductions to normal forms using a transducer operating on tree encodings of a cyclic representation of zippers. A zipper is a data structure introduced by Gérard Huet for representing a subtree together with its context, i.e. it is a tree with a focus that points to some node inside it. We mention some potential applications of this representation of attribute grammars as zipper transformers

An Actor-Oriented and Architecture-Driven Approach for Spatially Explicit Agent-Based Modeling

Nowadays, there is an increasing need to rapidly build more realistic models to solve environmental problems in an interdisciplinary context. In particular, agent-based and spatial modeling have proven to be useful for understanding land use and land cover change processes. Both approaches include simulation platforms often used in several research domains to develop models explaining and analyzing complex phenomena. Domain experts generally use an ad hoc approach for model development, which relies on a code-and-fix life cycle, going from a prototype model through progressive refinement. This adaptive approach does not capture systematically actors’ knowledge and their interactions with the environment. The development and maintenance of resulting models become cumbersome and time-consuming. In this article, we propose an actor and architecture-driven approach that relies on relevant existing methods and satisfies the needs of spatially explicit agent-based modeling and implementation. We have designed an Agent Global Experiment framework incorporating a meta-model built from actor, agent architecture, and spatial concepts to produce an initial model from specifications provided by domain experts and system analysts. An engine is built as a tool to support model transformation. Domain knowledge including spatial specifications is summarized in a class diagram which is later transformed into the agent-based model. Finally, the XML file representing the model produced is used as input in the transformation process leading to code. This approach is illustrated on a hunting and population dynamic model to generate a running code for GAMA, an agent-based and spatially explicit simulation platform

Dynamique du sorgho de contre saison et potentialités des sols en zone de savane de l'Extrême-Nord du Cameroun

Dans les plaines de l'Extrême-Nord du Cameroun, la culture du "Muskuwaari", sorgho de contre saison connaît depuis les deux dernières décennies un engouement de plus en plus croissant des producteurs qui commencent à la pratiquer au-delà des terres traditionnelles sur vertisols adaptées à la culture. Toutefois, l'évolution de l'extension spatiale n'a pas encore été maîtrisée et les facteurs qui déterminent ce processus à l'échelle régionale sont complexes. Cette étude qui porte sur une zone de référence autour de la ville Maroua, vise d'abord à analyser les limites actuelles de cette extension et de fournir ensuite des éléments de compréhension de cette dynamique. Le croisement de la carte d'aptitude potentielle des sols avec celle des sites d'extension de la culture sous un SIG permet de se rendre compte qu'une importante partie, (soit 61% en 1987 et 76% en 1999) des meilleures terres ont déjà été défrichées principalement pour l'installation des champs de muskuwaari. L'interprétation des images satellites et les observations de terrain, confirment que le processus d'extension spatiale est en cours d'achèvement. Dans certaines zones, la forte demande en produits vivriers liée à la croissance démographique et les spéculations de plus en plus importantes effectuées par certains producteurs contribuent à une appropriation totale des meilleures terres et amènent certains à étendre la culture sur des sols reconnus peu propices. II est évident que dans un avenir proche, l'extension des superficies ne sera plus une alternative. La voie d'intensification est souhaitable mais reste hypothétique, car nécessite un appui organisationnel et technique. (Résumé d'auteur

Attribute Grammars as Recursion Schemes over Cyclic Representations of Zippers

International audienceEvaluation of attributes w.r.t. an attribute grammar can be obtained by inductively computing a function expressing the dependencies of the synthesized attributes on inherited attributes. This higher-order functional approach to attribute grammars leads to a straightforward implementation using a higher-order lazy functional language like Haskell. The resulting evaluation functions are, however, not easily amenable to optimization rules. We present an alternative first-order functional interpretation of attribute grammars where the input tree is replaced with an extended cyclic tree each node of which is aware of its context viewed as an additional child tree. By the way, we demonstrate that these cyclic representations of zippers (trees with their context) are natural generalizations of doubly-linked lists to trees over an arbitrary signature