Jacques Chabin

Narrowing Directed by a Graph of Terms

Narrowing provides a complete procedure to solve equations modulo confluent and terminating rewriting systems. But it seldom terminates. This paper presents a method to improve the termination. The idea consists in using a finite graph of terms built from the rewriting system and the equation to be solved, which helps one to know the narrowing derivations possibly leading to solutions. Thus, the other derivations are not computed. This method is proved complete. An example is given and some improvements are proposed.

Visibly Pushdown Languages and Term Rewriting

To combine tree languages with term rewriting, we introduce a new class of tree languages, that both extends regular languages and restricts context-free languages, and that is closed under intersection (unlike context-free languages). To do it, we combine the concept of visibly pushdown language, with top-down pushdown tree automata, and we get the visibly pushdown tree automata. Then, we use them to express the sets of descendants for a sub-class of growing term rewrite systems, and thanks to closure under intersection, we get that joinability and (restricted) unifiability are decidable.

Over-approximating Descendants by Synchronized Tree Languages

Over-approximating the descendants (successors) of a initial set of terms by a rewrite system is used in verification. The success of such verification methods depends on the quality of the approximation. To get better approximations, we are going to use non-regular languages. We present a procedure that always terminates and that computes over-approximation of descendants, using synchronized tree-(tuple) languages expressed by logic programs.

Towards More Precise Rewriting Approximations

To check a system, some verification techniques consider a set of terms \(I\) that represents the initial configurations of the system, and a rewrite system \(R\) that represents the system behavior. To check that no undesirable configuration is reached, they compute an over-approximation of the set of descendants (successors) issued from \(I\) by \(R\), expressed by a tree language. Their success highly depends on the quality of the approximation. Some techniques have been presented using regular tree languages, and more recently using non-regular languages to get better approximations: using context-free tree languages [16] on the one hand, using synchronized tree languages [2] on the other hand. In this paper, we merge these two approaches to get even better approximations: we compute an over-approximation of the descendants, using synchronized-context-free tree languages expressed by logic programs. We give several examples for which our procedure computes the descendants in an exact way, whereas the former techniques compute a strict over-approximation.

Conservative type extensions for XML data

We introduce a method for building a minimal XML type (belonging to standard class of regular tree grammars) as an extension of other given types. Not only do we propose an easy-to-handle XML type evolution method, but we prove that this method computes the smallest extension of a given tree grammar, respecting pre-established constraints. We also adapt our technique to an interactive context, where an advised user is guided to build a new XML type from existing ones. A basic prototype of our tool is implemented.

Minimal tree language extensions: a keystone of XML type compatibility and evolution

In this paper, we propose algorithms that extend a given regular tree grammar G0 to a new grammar G respecting the following two properties: (i) G belongs to the sub-class of local or single-type tree grammars and (ii) G is the least grammar (in the sense of language inclusion) that contains the language of G0. Our algorithms give rise to important tools in the context of web service composition or XML schema evolution. We are particularly interested in applying them in order to reconcile different XML type messages among services. The algorithms are proven correct and some of their applications are discussed.

A ToolBox for Conservative XML Schema Evolution and Document Adaptation

We propose an algorithm that computes a mapping to obtain a conservative extension of original local schemas. This mapping ensures schema evolution and guides the construction of a document translator.

Validating Data from Semantic Web Providers

As the Linked Open Data and the number of semantic web data providers hugely increase, so does the critical importance of the following question: how to get usable results, in particular for data mining and data analysis tasks? We propose a query framework equiped with integrity constraints that the user wants to be verified on the results coming from semantic web data providers. We precise the syntax and semantics of those user quality constraints. We give algorithms for their dynamic verification during the query computation, we evaluate their performance with experimental results, and discuss related works.

CDR: A Rewriting Based Tool to Design FPLA Circuits

A rewriting based method to design circuits on FPLA electronic devices is presented. It is an improvement of our previous work. In comparison with this latter, the number of boolean vectors generated during the design process is reduced. This is done thanks to new forms of rewriting rules denoting new interesting properties on boolean vectors, associated to boolean products. Only boolean products which are implicants of the circuit to design are computed. Thus, this new design process is more efficient than the previous one.

A Context-driven Querying System for Urban Graph Analysis

This paper presents a context-driven query system for urban computing where users are responsible for defining their own restrictions over which datalog-like queries are built. Instead of imposing constraints on databases, our goal is to filter consistent data during the query process. Our query language is able to express aggregates in recursive rules, allowing it to capture network properties typical of graph analysis. This paper presents our query system and analyzes its capabilities using use cases in Urban Computing.