• WK seminar

In massively collaborative projects such as scientific or community databases, users often need to agree or disagree on the content of individual data items. On the other hand, trust relationships often exist between users, allowing them to accept or reject other users' beliefs by default. As those trust relationships become complex, however, it becomes difficult to define and compute a consistent snapshot of the conflicting information. Previous solutions to a related problem, the update reconciliation problem, are dependent on the order in which the updates are processed and, therefore, do not guarantee a globally consistent snapshot. This paper proposes the first principled solution to the automatic conflict resolution problem in a community database. Our semantics is based on the certain tuples of all stable models of a logic program. While evaluating stable models in general is well known to be hard, even for very simple logic programs, we show that the conflict resolution problem admits a PTIME solution. To the best of our knowledge, ours is the first PTIME algorithm that allows conflict resolution in a principled way. We further discuss extensions to negative beliefs and prove that some of these extensions are hard. This work is done in the context of the BeliefDB project at the University of Washington, which focuses on the efficient management of conflicts in community databases. PROJECT WEB PAGE http://db.cs.washington.edu/beliefDB/

• Event: "Enjeux de Modélisation et Analyse Liés aux Problèmes de Surfaces Rugueuses et de Défauts" (2010)

• Event: "Enjeux de Modélisation et Analyse Liés aux Problèmes de Surfaces Rugueuses et de Défauts" (2010)

• Event: "Enjeux de Modélisation et Analyse Liés aux Problèmes de Surfaces Rugueuses et de Défauts" (2010)

• Event: "Enjeux de Modélisation et Analyse Liés aux Problèmes de Surfaces Rugueuses et de Défauts" (2010)

• Event: "Enjeux de Modélisation et Analyse Liés aux Problèmes de Surfaces Rugueuses et de Défauts" (2010)

• Event: "Enjeux de Modélisation et Analyse Liés aux Problèmes de Surfaces Rugueuses et de Défauts" (2010)

• Event: "Enjeux de Modélisation et Analyse Liés aux Problèmes de Surfaces Rugueuses et de Défauts" (2010)

• Event: "Enjeux de Modélisation et Analyse Liés aux Problèmes de Surfaces Rugueuses et de Défauts" (2010)

• Event: "Enjeux de Modélisation et Analyse Liés aux Problèmes de Surfaces Rugueuses et de Défauts" (2010)

• Event: "Enjeux de Modélisation et Analyse Liés aux Problèmes de Surfaces Rugueuses et de Défauts" (2010)

• Event: "Enjeux de Modélisation et Analyse Liés aux Problèmes de Surfaces Rugueuses et de Défauts" (2010)

• Event: "Enjeux de Modélisation et Analyse Liés aux Problèmes de Surfaces Rugueuses et de Défauts" (2010)

• Event: "Enjeux de Modélisation et Analyse Liés aux Problèmes de Surfaces Rugueuses et de Défauts" (2010)

• Event: "Enjeux de Modélisation et Analyse Liés aux Problèmes de Surfaces Rugueuses et de Défauts" (2010)

• Event: "Enjeux de Modélisation et Analyse Liés aux Problèmes de Surfaces Rugueuses et de Défauts" (2010)

We consider a model describing an experimental setting, in which locusts run in a ring-shaped arena. With intermediate spatial density of the individuals, coherent motion is observed, interrupted by sudden changes of direction ("switching"). Contrary to the known model of Czirok and Vicsek, our model assumes runs of the individuals in either positive or negative direction of the 1D arena with the same speed, that are subject to random switches. As supported by experimental evidence, the individual switching frequency increases in response to a local or global loss of group alignment, which constitutes a mechanism to increase the coherence of the group. We show that our individual based model, although phenomenologically very simple, exhibits nontrivial dynamics with a "phase change" behaviour, and, in particular, recovers the observed group directional switching. Passing to the corresponding Fokker-Planck equation, we are able to give estimates of the expected switching times in terms of number of individuals and values of the model coefficients. Then we pass to the kinetic description, recovering a system of two kinetic equations with nonlocal and nonlinear right hand sides, which is valid when the number of individuals tends to infinity. We perform a mathematical analysis of the system, show some numerical results and point out several interesting open problems.

• WK seminar