Yves Roos

Synchronized Shuffle and Regular Languages

New representation results for three families of regular languages are stated, using a special kind of shuffle operation, namely the synchronized shuffle. First, it is proved that the family of regular star languages is the smallest family containing the language (a + bc)* and closed under synchronized shuffle and length preserving morphism. The second representation result states that the family of e-free regular languages is the smallest family containing the language (a + bc)*d and closed under synchronized shuffle, union and length preserving morphism. At last, it is proved that Reg is the smallest family containing the two languages (a+ bb)* and a+(ab)+, closed under synchronized shuffle, union and length preserving morphism.

View update translation for XML

We study the problem of update translation for views on XML documents. More precisely, given an XML view definition and a user defined view update program, find a source update program that translates the view update without side effects on the view. Additionally, we require the translation to be defined on all possible source documents; this corresponds to Hegners notion of uniform translation. The existence of such translation would allow to update XML views without the need of materialization. The class of views we consider can remove parts of the document and rename nodes. Our update programs define the simultaneous application of a collection of atomic update operations among insertion/deletion of a subtree and node renaming. Such update programs are compatible with the XQuery Update Facility (XQUF) snapshot semantics. Both views and update programs are represented by recognizable tree languages. We present as a proof of concept a small fragment of XQUF that can be expressed by our update programs, thus allows for update propagation. Two settings for the update problem are studied: without source constraints, where all source updates are allowed, and with source constraints, where there is a restricted set of authorized source updates. Using tree automata techniques, we establish that without constraints, all view updates are uniformly translatable and the translation is tractable. In presence of constraints, not all view updates are uniformly translatable. However, we introduce a reasonable restriction on update programs for which uniform translation with constraints becomes possible.

Static analysis of XML security views and query rewriting

In this paper, we revisit the view based security framework for XML without imposing any of the previously considered restrictions on the class of queries, the class of DTDs, and the type of annotations used to define the view. First, we study query rewriting with views when the classes used to define queries and views are Regular XPath and MSO. Next, we investigate problems of static analysis of security access specifications (SAS): we introduce the novel class of interval-bounded SAS and we define three different manners to compare views (i.e. queries) from a security point of view. We provide a systematic study of the complexity for deciding these three comparisons, when the depth of the XML documents is bounded, when the document may have an arbitrary depth but the queries defining the views are restricted to guarantee the interval-bounded property, and in the general setting without restriction on queries and document.

Semi-Commutations and Rational Expressions

We extend the notion of concurrent iteration defined on trace languages by E.Ochmanski to languages closed under a semi-commutation relation which is the non-symmetric version of partial commutation relation: we iterate strongly connected components of words. For a given semi-commutation relation, this leads to the definition of a new family of rational languages closed under the semi-commutation. We give a necessary and sufficient condition for a language closed under a semi-commutation relation to be a rational language and we proved that the equality between the families of rational languages and recognizable languages closed under a semi-commutation relation is true if and only if the semi-commutation is symmetric (i.e a partial commutation).

Synchronization languages

Synchronization expressions introduced in [7] within the framework of the Pm-C project are a high-level construct which allow a programmer to express minimal synchronization constraints of a program in a distributed context. The study and the implementation of these expressions are based on their associated synchronization languages. Synchronization languages have been introduced in [9, lo]. They give a way to implement synchronization expressions and specify their semantic. These languages represent distributed systems whose behaviour respects synchronization constraints expressed by the programmer with synchronization expressions. So these languages describe all the correct executions of a program. In [9, lo] Guo, Salomaa and Yu propose a characterization of synchronization languages based on a rewriting system named R which generalizes partial commutations. This system gives a way to rewrite a word representing a parallel execution into a word with a lower or equal degree of parallelism. Guo et al. show that every synchronization language is closed under the system R and they conjecture that it is sufficient for a regular language to be closed under R to be a synchronization language. We show that the conjecture is true in the particular case of languages expressing the synchronization between two distinct actions. We also show that the conjecture is false in the general case. @ 1999-Elsevier Science B.V. All rights reserved

Decomposition of Partial Commutations

We define atomic partial commutations that are associated to independence relations of the form A1×A2 ∪ A2×A1 where A1, A2 are two disjoint subsets of the alphabet. Then we prove that each partial commutation can be obtained as the composition of atomic partial commutations.

A canonical automaton for one-rule length-preserving string rewrite systems

In this work, we use rearrangements in rewriting positions sequence in order to study precisely the structure of the derivations in one-rule length-preserving string rewrite systems. That yields to the definition of a letter-to-letter transducer that computes the relation induced by a one-rule length-preserving string rewrite system. This transducer can be seen as an automaton over an alphabet A × A . We prove that this automaton is finite if and only if the corresponding relation is rational. We also identify a sufficient condition for the context-freeness of the language L recognized by this automaton and, when this condition is satisfied, we construct a pushdown automaton that recognizes L.

Semi-commutations and Partial Commutations

The aim of this paper is to show that a semi-commutation function can be expressed as the compound of a sequential transformation, a partial commutation function, and the reverse transformation. Moreover, we give a necessary and sufficient condition for the image of a regular language to be computed by the compound of two sequential functions and a partial commutation function.