Event Systems and Access Control

We consider the interpretations of notions of access control (permissions, interdictions, obligations, and user rights) as run-time properties of information systems specified as event systems with fairness. We give proof rules for verifying that an access control policy is enforced in a system, and consider preservation of access control by refinement of event systems. In particular, refinement of user rights is non-trivial; we propose to combine low-level user rights and system obligations to implement high-level user rights

Threshold Behaviour in Gauge Boson Pair Production at LEP 2

We discuss the form of the amplitude for gauge boson pair production at or near threshold.We show that in the case of W-pair production at LEP2 near threshold only one anomalous electromagnetic coupling can contribute. This anomalous coupling is CP violating and contributes to the electric dipole moment of the $W$. Since this coupling is likely to be small, it is important to look for ZZgamma couplings in Zgamma production. These couplings are not suppressed at the W-threshold

Modelling an Aircraft Landing System in Event-B (Full Report)

The failure of hardware or software in a critical system can lead to loss of lives. The design errors can be main source of the failures that can be introduced during system development process. Formal techniques are an alternative approach to verify the correctness of critical systems, overcoming limitations of the traditional validation techniques such as simulation and testing. The increasing complexity and failure rate brings new challenges in the area of verification and validation of avionic systems. Since the reliability of the software cannot be quantified, the \textit{correct by construction} approach can implement a reliable system. Refinement plays a major role to build a large system incrementally from an abstract specification to a concrete system. This paper contributes as a stepwise formal development of the landing system of an aircraft. The formal models include the complex behaviour, temporal behaviour and sequence of operations of the landing gear system. The models are formalized in Event-B modelling language, which supports stepwise refinement. This case study is considered as a benchmark for techniques and tools dedicated to the verification of behavioural properties of systems. The report is the full version of a paper published for the ABZ 2014 Case Study. i

What can the L3 γγll\gamma\gamma ll events be?

We consider the 4 $\gamma\gamma ll$ ($l=\mu,\ e$) events reported by the L3 collaboration, and go through the logical possibilities which could explain the events. If they are not coincidental bremsstrahlung events, we find that the physics which they could point to is extremely limited. One possibility would be to have a new 60 GeV scalar (or pseudoscalar) particle $X^0$ with an off-diagonal coupling to a $Z$ and $Z'$ which is non-perturbative ($\alpha > 1$), where the $Z'$ couplings to $\nu\bar\nu$ are suppressed. One could also construct a model involving $X^0$, and a second scalar $X'^0$ with a large $X'll$ coupling. We do not promote either of these models, but hope they would prove to be useful guidelines, should the L3 events turn out to be new physics.Comment: 7 pp (3 fig avail. on request), LATEX, TRI-PP-92-12

Generating Distributed Programs from Event-B Models

Distributed algorithms offer challenges in checking that they meet their specifications. Verification techniques can be extended to deal with the verification of safety properties of distributed algorithms. In this paper, we present an approach for combining correct-by-construction approaches and transformations of formal models (Event-B) into programs (DistAlgo) to address the design of verified distributed programs. We define a subset LB (Local Event-B) of the Event-B modelling language restricted to events modelling the classical actions of distributed programs as internal or local computations, sending messages and receiving messages. We define then transformations of the various elements of the LB language into DistAlgo programs. The general methodology consists in starting from a statement of the problem to program and then progressively producing an LB model obtained after several refinement steps of the initial LB model. The derivation of the LB model is not described in the current paper and has already been addressed in other works. The transformation of LB models into DistAlgo programs is illustrated through a simple example. The refinement process and the soundness of the transformation allow one to produce correct-by-construction distributed programs.Comment: In Proceedings VPT/HCVS 2020, arXiv:2008.0248

Proving Distributed Algorithms by Combining Refinement and Local Computations

Distributed algorithms are considered to be very complex to design and to prove; our paper contributes to the design of correct-by-construction distributed algorithms. The main idea relies upon the development of distributed algorithms following a top/down approach, which is clearly well known in earlier works of Dijkstra, and to use refinement for proving the correctness of the resulting algorithms. However, the link between the problem and the first model remains to be expressed and the refinement is a real help to justify in a very progressive way the choices of design. We propose in this work a framework combining local computations models and refinement to prove the correctness of a large class of distributed algorithms. Local computations models define abstract computing processes for solving problems by distributed algorithms and can be integrated into a the Event-B modelling language to define proof-based patterns for the design of distributed algorithms. We illustrate our approach by examples like the leader election protocol or the distributed coloring algorithm. Our proposal is integrated into an environment called ViSiDiA

Avranches – Le Grand Doyenné

Lien Atlas (MCC) :http://atlas.patrimoines.culture.fr/atlas/trunk/index.php?ap_theme=DOM_2.01.02&ap_bbox=-1.377;48.675;-1.336;48.702 Dans le cadre des recherches qui se poursuivent au Grand Doyenné, un sondage archéologique a été réalisé, en octobre 2013, afin de vérifier la présence de structures disparues, côté cour, au sud de l’édifice. À l’époque de sa construction, au xiie s., le Grand Doyenné est un bâtiment constitué par un volume unique qu’occupe une vaste salle d’apparat accessible d..

Teaching programming methodology using Event B

International audienceEvent B is supported by the RODIN platform and provides a framework for teaching programming methodology based on the famous pre/post specifications, together with the refinement. We illustrate a methodology based on Event B and the refinement by developing Floyd's algorithm for computing the shortest distances of a graph, which is based on an algorithm design technique called dynamic programming. The development is based on a paradigm identifying a non-deterministic event with a procedure call and by introducing control states. We discuss points related to our lectures at the university