École normale supérieure de Cachan

About: École normale supérieure de Cachan is a education organization based out in Cachan, Île-de-France, France. It is known for research contribution in the topics: Decidability & Nonlinear system. The organization has 2717 authors who have published 5585 publications receiving 175925 citations.

Future-Looking Logics on Data Words and Trees

Abstract: In a data word or a data tree each position carries a label from a finite alphabet and a data value from an infinite domain Over data words we consider the logic ${\sf LTL}^{\downarrow}_{1}(\rm F)$, that extends LTL( F) with one register for storing data values for later comparisons We show that satisfiability over data words of ${\sf LTL}^{\downarrow}_{1}(\rm F)$ is already non primitive recursive We also show that the extension of ${\sf LTL}^{\downarrow}_{1}(\rm F)$ with either the backward modality F ? 1 or with one extra register is undecidable All these lower bounds were already known for ${\sf LTL}^{\downarrow}_{1}({\rm X,F})$ and our results essentially show that the X modality was not necessary Moreover we show that over data trees similar lower bounds hold for certain fragments of Xpath

XML with incomplete information

Abstract: We study models of incomplete information for XML, their computational properties, and query answering. While our approach is motivated by the study of relational incompleteness, incomplete information in XML documents may appear not only as null values but also as missing structural information. Our goal is to provide a classification of incomplete descriptions of XML documents, and separate features—or groups of features—that lead to hard computational problems from those that admit efficient algorithms. Our classification of incomplete information is based on the combination of null values with partial structural descriptions of documents. The key computational problems we consider are consistency of partial descriptions, representability of complete documents by incomplete ones, and query answering. We show how factors such as schema information, the presence of node ids, and missing structural information affect the complexity of these main computational problems, and find robust classes of incomplete XML descriptions that permit tractable query evaluation.