A systematic approach to atomicity decomposition in Event-B

Event-B is a state-based formal method that supports a refinement process in which an abstract model is elaborated towards an implementation in a step-wise manner. One weakness of Event-B is that control flow between events is typically modelled implicitly via variables and event guards. While this fits well with Event-B refinement, it can make models involving sequencing of events more difficult to specify and understand than if control flow was explicitly specified. New events may be introduced in Event-B refinement and these are often used to decompose the atomicity of an abstract event into a series of steps. A second weakness of Event-B is that there is no explicit link between such new events that represent a step in the decomposition of atomicity and the abstract event to which they contribute. To address these weaknesses, atomicity decomposition diagrams support the explicit modelling of control flow and refinement relationships for new events. In previous work,the atomicity decomposition approach has been evaluated manually in the development of two large case studies, a multi media protocol and a spacecraft sub-system. The evaluation results helped us to develop a systematic definition of the atomicity decomposition approach, and to develop a tool supporting the approach. In this paper we outline this systematic definition of the approach, the tool that supports it and evaluate the contribution that the tool makes

Practical Theory Extension in Event-B

Abstract. The Rodin tool for Event-B supports formal modelling and proof using a mathematical language that is based on predicate logic and set theory. Although Rodin has in-built support for a rich set of operators and proof rules, for some application areas there may be a need to extend the set of operators and proof rules supported by the tool. This paper outlines a new feature of the Rodin tool, the theory component, that allows users to extend the mathematical language supported by the tool. Using theories, Rodin users may define new data types and polymorphic operators in a systematic and practical way. Theories also allow users to extend the proof capabilities of Rodin by defining new proof rules that get incorporated into the proof mechanisms. Soundness of new definitions and rules is provided through validity proof obligations.

A L\'evy area by Fourier normal ordering for multidimensional fractional Brownian motion with small Hurst index

The main tool for stochastic calculus with respect to a multidimensional process $B$ with small H\"older regularity index is rough path theory. Once $B$ has been lifted to a rough path, a stochastic calculus -- as well as solutions to stochastic differential equations driven by $B$ -- follow by standard arguments. Although such a lift has been proved to exist by abstract arguments \cite{LyoVic07}, a first general, explicit construction has been proposed in \cite{Unt09,Unt09bis} under the name of Fourier normal ordering. The purpose of this short note is to convey the main ideas of the Fourier normal ordering method in the particular case of the iterated integrals of lowest order of fractional Brownian motion with arbitrary Hurst index.Comment: 20 page

Transforming Event-B models to Dafny contracts

Our work aims to build a bridge between constructive (top-down) and analytical (bottom-up) approaches to software verification. This paper presents a tool-supported method for linking two existing verification methods: Event-B (constructive) and Dafny (analytical). This method combines Event-B abstraction and refinement with the code-level verification features of Dafny. The link transforms Event-B models to Dafny contracts by providing a framework in which Event-B models can be implemented correctly. The paper presents a method for transformation of Event-B models of abstract data types to Dafny contracts. Also a prototype tool implementing the transformation method is outlined. The paper also defines and proves a formal link between property verification in Event-B and Dafny. Our approach is illustrated with a small case study

Stability of solutions to some evolution problem

Large time behavior of solutions to abstract differential equations is studied. The corresponding evolution problem is: $$\dot{u}=A(t)u+F(t,u)+b(t), \quad t\ge 0; \quad u(0)=u_0. \qquad (*)$$ Here $\dot{u}:=\frac {du}{dt}$, $u=u(t)\in H$, $t\in \R_+:=[0,\infty)$, $A(t)$ is a linear dissipative operator: Re$(A(t)u,u)\le -\gamma(t)(u,u)$, $\gamma(t)\ge 0$, $F(t,u)$ is a nonlinear operator, $\|F(t,u)\|\le c_0\|u\|^p$, $p>1$, $c_0,p$ are constants, $\|b(t)\|\le \beta(t),$ $\beta(t)\ge 0$ is a continuous function. Sufficient conditions are given for the solution $u(t)$ to problem (*) to exist for all $t\ge0$, to be bounded uniformly on $\R_+$, and a bound on $\|u(t)\|$ is given. This bound implies the relation $\lim_{t\to \infty}\|u(t)\|=0$ under suitable conditions on $\gamma(t)$ and $\beta(t)$. The basic technical tool in this work is the following nonlinear inequality: $$ \dot{g}(t)\leq -\gamma(t)g(t)+\alpha(t,g(t))+\beta(t),\ t\geq 0;\quad g(0)=g_0. $

ViBe (Virtual Berlin) - Immersive Interactive 3D Urban Data Visualization - Immersive interactive 3D urban data visualization

The project investigates the possibility of visualizing open source data in a 3D interactive virtual environment. We propose a new tool, 'ViBe'. We programmed 'ViBe' using Unity for its compatibility with HTC VIVE glasses for virtual reality (VR). ViBe offers an abstract visualization of open source data in a 3D interactive environment. The ViBe environment entails three main topics a) inhabitants, b) environmental factors, and c) land-use; acting as representatives of parameters for cities and urban design. Berlin serves as a case study. The data sets used are divided according to Berlin's twelve administrative districts. The user immerses into the virtual environment where they can choose, using the HTC Vive controllers, which district (or Berlin as a whole) they want information for and which topics they want to be visualized, and they can also teleport back and forth between the different districts. The goal of this project is to represent different urban parameters an abstract simulation where we correlate the corresponding data sets. By experiencing the city through visualized data, ViBe aims to provide the user with a clearer perspective onto the city and the relationship between its urban parameters. ViBe is designed for adults and kids, urban planners, politicians and real estate developers alike