Showing papers by "Jean Moulin University Lyon 3 published in 2001"
TL;DR: Every fiber-complemented graph without isometric ray contains a Cartesian product of elementary graphs which is invariant under every automorphism, and this theory gives a global approach to obtain several previous results related to median graphs, quasi-median graphs, pseudo-medians, weakly Median graphs, bridged graphs, and extend them to the infinite case.
25 citations
TL;DR: Many properties about (strongly) Helly graphs are known, in particular results concerning the geodesic convexity and fixed point properties or more precisely invariant simplex properties are surveyed.
13 citations
13 Nov 2001
TL;DR: A role-based object model is proposed to describe the local data access security schemas ( Discretionary and non-discretionary models) to solve some of the problems of federated information systems with loose coupling among local data sources.
Abstract: Data access security in federated information systems with loose coupling among local data sources is hard to achieve mainly for two reasons: local data information source heterogeneity (data models, access security models, semantics...), local autonomy which do not allow to create a global integrated consistent security schema. To solve some of such problems we propose a role-based object model to describe the local data access security schemas (discretionary and non-discretionary models). Interoperability among the various local data sources is achieved by a rich descriptive layer at the federated level. The global security policy allows to define the choices concerning information flow control both for importation (from the federation to a local system) and exportation (from a local system to the federation).
11 citations
20 Apr 2001
1 citations
TL;DR: In this paper, it was shown that a countable connected graph has an end-faithful spanning tree that contains a prescribed set of rays whenever this set is countable, and this solution is, in a certain sense, the best possible.
Abstract: We prove that a countable connected graph has an end-faithful spanning tree that contains a prescribed set of rays whenever this set is countable, and we show that this solution is, in a certain sense, the best possible. This improves a result of Hahn and Siran [2, Theorem 1]