Designing optimal- and fast-on-average pattern matching algorithms

Given a pattern $w$ and a text $t$, the speed of a pattern matching algorithm over $t$ with regard to $w$, is the ratio of the length of $t$ to the number of text accesses performed to search $w$ into $t$. We first propose a general method for computing the limit of the expected speed of pattern matching algorithms, with regard to $w$, over iid texts. Next, we show how to determine the greatest speed which can be achieved among a large class of algorithms, altogether with an algorithm running this speed. Since the complexity of this determination make it impossible to deal with patterns of length greater than 4, we propose a polynomial heuristic. Finally, our approaches are compared with 9 pre-existing pattern matching algorithms from both a theoretical and a practical point of view, i.e. both in terms of limit expected speed on iid texts, and in terms of observed average speed on real data. In all cases, the pre-existing algorithms are outperformed

Mapping sequences by parts

© 2007 Didier and Guziolowski; licensee BioMed Central Ltd

Cooling sequences and color-magnitude diagrams for cool white dwarfs with hydrogen-atmospheres

We present new cooling sequences, color-magnitude diagrams, and color-color diagrams for cool white dwarfs with pure hydrogen atmospheres down to an effective temperature \te=1500 K. We include a more detailed treatment of the physics of the fully-ionized interior, particularly an improved discussion of the thermodynamics of the temperature-dependent ion-ion and ion-electron contributions of the quantum, relativistic electron-ion plasma. The present calculations also incorporate accurate boundary conditions between the degenerate core and the outermost layers as well as updated atmosphere models including the H$_2$-H$_2$ induced-dipole absorption. We examine the differences on the cooling time of the star arising from uncertainties in the initial carbon-oxygen profile and the core-envelope $L$-$T_c$ relation. The maximum time delay due to crystallization-induced chemical fractionation remains substantial, from $\sim 1.0$ Gyr for 0.5 and 1.2 \msol white dwarfs to $\sim 1.5$ Gyr for 0.6 to 0.8 \msol white dwarfs, even with initial stratified composition profiles, and cannot be ignored in detailed white dwarf cooling calculations. These cooling sequences provide theoretical support to search for or identify old disk or halo hydrogen-rich white dwarfs by characterizing their mass and age from their observational signatures.Comment: 43 pages, Latex file, uses aasms4.sty, accepted for publication in ApJ (November 10 issue

Analyse comparative de corpus : cas de l'ingénierie des connaissances

We describe a real experiment in order to build a thematic index of a scientific book. This book is a compilation of 21 articles from the French Knowledge Engineering conferences (1999-2001). The corpus has been analysed by SYNTEX then by INDDOC, software dedicated to index formation. This work has been realized in a full digital context, with digital HTML articles and HTML index. The user uses a browser for exploring the articles through the index. We describe the work, the main problems and the chosen solutions.Dans cet article, nous présentons une analyse de l'évolution du domaine de recherche de l'Ingénierie des connaissances telle qu'elle peut être saisie par l'étude comparative de deux corpus de textes représentatifs du domaine et chronologiquement successifs. La méthode utilisée, une analyse lexicale constrastive, s'appuie sur l'hypothèse que les évolutions du vocabulaire utilisé dans ces deux corpus peuvent être la trace d'évolutions thématiques dans ce domaine de recherche. L'article présente les deux analyseurs utilisés (SYNTEX et UPERY) avant de détailler plusieurs des interprétations construites sur la base de différences de fréquence, de répartition et d'environnement contextuel des termes révélées par les outils

Dynamic Attribute Grammars

Projet OSCARAlthough Attribuate Grammars were introduced thirty years ago, their lack of expressiveness has resulted in limited use outside the domain of static language processing. With the new notion of a Dynamic Attribute Grammar defined on a Grammar Couple, informally presented in a previous paper, we show that it is possible to extend this expressiveness and to describe computations on structures that are not just trees, but also on abstractions allowing for infinite structures. The result is a language that is comparable in power to most first-order functional languages, with a distinctive declarative character. In this paper, we give a formal definition of Dynamic Attribute Grammars and show how to construct efficient visit-sequence-based evaluators for them, using traditional, well-established AG techniques (in our case, using the FNC2 system The major contribution of this approach is to restore the intrinsic power of Attribute Grammar and re-emphasize the effectiveness of analysis and implement- ation techniques developed for them

Attribute Grammars: a Declarative Functional Language

Projet CHARMEAlthough Attribute Grammars were introduced thirty years ago, their lack of expressiveness has resulted in limited use outside the domain of static language processing. In this paper we show that it is possible to extend this expressiveness. We claim that Attribute Grammars can be used to describe computations on structures that are not just trees, but also on abstractions allowing for infinite structures. To gain this expressiveness, we introduce two new notions: {\em scheme productions\/} and {\em conditional productions}. The result is a language that is comparable in power to most first-order functional languages, with a distinctive declarative character. Our extensions deal with a different part of the Attribute Grammars formalism than what is used in most works on Attribute Grammars including global analysis and evaluator generation. Hence, most existing results are directly applicable to our extended Attribute Grammars including efficient implementation (in our case, using the FNC-2 system http://www-rocq.inria.fr/charme/FNC-2/). The major contribution of this approach is to restore and re-emphasize the intrinsic power of Attribute Grammars. Furthermore, our extensions call for new studies on applying to functional programming the analysis and implementation techniques developed for Attribute Grammars

Structure-directed Genericity in Functional Programming and Attribute Grammars

Projet OSCARGeneric control operators, such as \emph{fold}, have been introduced in functional programming to increase the power and applicability of data-structure-based transformations. This is achieved by making the structure of the data more explicit in program specifications. We argue that this very important property is one of the original concepts of attribute grammars. In this paper, we present the similarities between the \emph{fold} formalism and attribute grammars. In particular, we show the equivalence of their respective deforestation methods. Given these results and the fundamental role of deforestation in the concept of \emph{structure-directed genericity}, first devised for attribute grammars with descriptional composition, we show how the \emph{fold} operator with its fusion method allow us to transport this concept in the area of functional programming