10,446 research outputs found
Applying Atomicity and Model Decomposition to a Space Craft System in Event-B
No full textEvent-B is a formal method for modeling and verifying consistency of systems. In formal methods such as Event-B, refinement is the process of enriching or modifying an abstract model in a step-wise manner in order to manage the development of complex and large systems. To further alleviate the complexity of developing large systems, Event-B refinement can be augmented with two techniques, namely atomicity decomposition and model decomposition. Our main objective in this paper is to investigate and evaluate the application of these techniques when used in a refinement based development. These techniques have been applied to the formal development of a space craft system. The outcomes of this experimental work are presented as assessment results. The experience and assessment can form the basis for some guidelines in applying these techniques in future cases
Specification and refinement of discrete timing properties in Event-B
No full textEvent-B is a formal language for systems modeling, based on set theory and predicate logic. It has the advantage of mechanized proof, and it is possible to model a system in several levels of abstraction by using refinement. Discrete timing properties are important in many critical systems. However, modeling of timing properties is not directly supported in Event-B. In this paper we identify three main categories of discrete timing properties for trigger-response pattern, deadline, delay and expiry. We introduce language constructs for each of these timing properties that augment the Event-B language. We describe how these constructs can be mapped to standard Event-B constructs. To ease the process of using the timing constructs in a refinement-based development, we introduce patterns for refining the timing constructs that allow timing properties on abstract models to be replaced by timing properties on refined models. The language constructs and refinement patterns are illustrated through some generic examples. Event-B refinement allows atomic events at the abstract level to be broken down into sub-steps at the refined level. The goal of our refinement patterns is to provide an easy way to represent and correctly refine timing constraints on abstract atomic events with more elaborate timing constraints on the refined events. This paper presents an initial set of patterns
A systematic approach to atomicity decomposition in Event-B
No full textEvent-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
Decomposition Structures for Event-B
No full textAbstract. Event-B provides a flexible approach to modelling and re-finement of systems. In this paper we outline two important ways in which Event-B refinement can be augmented with additional structuring to support further the management of complex refinements. Firstly we show how event refinement diagrams can be used to structure refinement steps involving decomposition of atomicity. Secondly we outline a tech-nique for decomposing models into sub-models to allow for independent refinement. We show how these two structuring techniques can be used together.
Automatic Refinement Checking for B
No full textRefinement is a key concept in the B-Method. While refinement is at the heart of the B Method, so far no automatic refinement checker has been developed for it. In this paper we present a refinement checking algorithm and implementation for B. It is based on using an operational semantics of B, obtained in practice by the ProB animator. The refinement checker has been integrated into ProB toolset and we present various case studies and empirical results in the paper, showing the algorithm to be surprisingly effective. The algorithm checks that a refinement preserves the trace properties of a specification. We also compare our tool against the refinement checker FDR for CSP and discuss an extension for singleton failure refinement
Composing Event-B Specifications - Case-Study Experience
No full textEvent-B is a formal method, based on set theory and first-order logic, for specification and verification of reactive systems supported by the Rodin tool kit. Feature modelling is a well-known technique for managing variability and configuring products within software product lines (SPLs). Our objective is to explore whether we can use existing Event-B composition techniques and tooling for feature-based product line development. If case-study experiments reveal these mechanisms to be inadequate, then they also should suggest further research directions. The main objective is to maximise the amount of reuse. This includes avoiding as far as possible having to reprove a composed specification when the models being composed have already been proven. We have modelled two case-studies in Event-B using both horizontal and vertical refinements. This work contributes by analysing existing tools and techniques in Event-B for feature-based development, exploring composition related issues by modelling example case-studies and suggesting further tooling requirements
Halting a Runaway Train: Reforming Teacher Pensions for the 21st Century
No full textWhen it comes to public-sector pensions, writes lead author Michael B. Lafferty in this report, "A major public-policy (and public-finance) problem has been defined and measured, debated and deliberated, but not yet solved. Except where it has been." As recounted in "Halting a Runaway Train: Reforming Teacher Pensions for the 21st Century", these exceptions turn out to be revealing -- and encouraging
ProB: A Model Checker for B
No full textWe present ProB, an animation and model checking tool for the B method. ProB's animation facilities allow users to gain confidence in their specifications, and unlike the animator provided by the B-Toolkit, the user does not have to guess the right values for the operation arguments or choice variables. ProB contains a model checker and a constraint-based checker, both of which can be used to detect various errors in B specifications. We present our first experiences in using ProB on several case studies, highlighting that ProB enables users to uncover errors that are not easily discovered by existing tools
Tools for system validation with B abstract machines
No full textIn this paper we give an overview of some tools that we have developed to support the application of the B Method. ProB is an animation and model checking tool for the B method. ProB's animation facilities allow users to gain confidence in their specifications. ProB contains a temporal and a state-based model checker, both of which can be used to detect various errors in B specifications. We also overview a recent extension of ProB that supports checking of specifications written in a combination of CSP and B. Finally we describe the UML-B profile and associated U2B tool that allows UML and B to be combined and is intended to make modelling with B more appealing to software engineers
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