Different Perspectives for Reasoning about Problems and Faults
Patterns for Modelling Time and Consistency in Business Information Systems
Maintaining semantic consistency of data is a significant problem in distributed information systems, particularly those on which a business may depend. Our current work aims to use Event-B and the Rodin tools to support the specification and design of such systems in a way that integrates well into existing development processes. This paper presents Event-B patterns that may be used to represent recovery from timebounded inconsistency and illustrates their use in a model derived from industrial applications.
Several safety-critical systems, such as avionic, transportation and space systems, use the notion of operation modes. Operation modes are useful structuring units that facilitate design, specially if used with state-based formal methods. However, modelling abstractions to support the specification, analysis and correct construction of modal systems are still lacking. The contribution of this paper is twofold: (i) modal systems and modal systems refinement are discussed and formalized; (ii) the relation of a modal system specification with an Event-B model is discussed, showing how to demonstrate that the behaviour of an Event-B model can satisfy a modal system.
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Supporting Reuse in Event B Development: Modularisation Approach
Recently, Space Systems Finland has undertaken formal Event B development of a part of on-board software for the BepiColombo space mission. As a result, lack of modularization mechanisms in Event B has been identified as a serious obstacle to scalability. One of the main benefit of modularization is that it allows us to decompose system models into components that can be independently developed. It also helps to manage complexity of models that in the industrial setting are usually very large and difficult to comprehend. On the other hand, modularization enables reuse of formally developed components in the formal product line development. In this paper we propose a conservative extension of Event B formalism to support modularization. We demonstrate how our approach can support reuse in the formal development in the space domain.
Applying Event and Machine Decomposition to a Flash-Based Filestore in Event-B
Event-B is a formal method used for specifying and reasoning about systems. Rodin is a toolset for developing system models in Event-B. Our experiment which is outlined in this paper is aimed at applying Event-B and Rodin to a flash-based filestore. Refinement is a useful mechanism that allows developers to sharpen models step by step. Two uses of refinement, feature augmentation and structural refinement, were employed in our development. Event decomposition and machine decomposition are techniques on which we focus in this work. We present an outline of a verified refinement chain for the flash filestore. We also outline evidence of the applicability of the method and tool together with some guidelines.
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While current studies on Web services composition are mostly focused - from the technical viewpoint - on standards and protocols, this work investigates the adoption of formal methods for dependable composition. The Web Services Business Process Execution Language (WS-BPEL) - an OASIS standard widely adopted both in academic and industrial environments - is considered as a touchstone for concrete composition languages and an analysis of its ambiguous Recovery Framework specification is offered. In order to show the use of formal methods, a precise and unambiguous description of its (simplified) mechanisms is provided by means of a conservative extension of the pi-calculus. This has to be intended as a well known case study providing methodological arguments for the adoption of formal methods in software specification. The aspect of verification is not the main topic of the paper but some hints are given.
A Formal Semantics for the WS-BPEL Recovery Framework: The pi-Calculus Way
Formal Development of the BepiColombo Pilot
This paper proposes a method for deriving formal specifications of systems. To accomplish this task we pass through a non trivial number of steps, concepts and tools where the first one, the most important, is the concept of method itself, since we realized that computer science has a proliferation of languages but very few methods. We also propose the idea of Layered Fault Tolerant Specification (LFTS) to make the method extensible to Dependable Systems. The principle is layering the specification, for the sake of clarity, in (at least) two different levels, the first one for the normal behavior and the others (if more than one) for the abnormal. The abnormal behavior is described in terms of an Error Injector (EI) which represents a model of the erroneous interference coming from the environment. This structure has been inspired by the notion of idealized fault tolerant component but the combination of LFTS and EI using rely guarantee thinking to describe interference can be considered one of the main contributions of this work. The progress toward this method and the way to layer specifications. has been made experimenting on the Transportation and the Automotive Case Studies of the DEPLOY project.
Deriving Specifications of Dependable Systems: toward a Method
Proposals for Mathematical Extensions for Event-B
Automated Property Verification for Large Scale B Models