Abstract

Abstract
The analysis of usability aspects of multi-user systems, such as co-operative work systems and pervasive systems, pose particular problems because group behavior of their users may have considerable impact on usability. Model-based analysis of such features leads to state-space explosion because of the sheer number of entities to be modeled when automatic techniques such as model checking are used. In this paper we explore the use of a recently proposed scalable model-based technique based on solving sets of Ordinary Differential Equations (ODEs). Starting from a formal model specified using the Performance Evaluation Process Algebra (PEPA), we show how different groupware usage patterns may be modeled and analyzed using this approach. We illustrate how the approach can explore different design options and their impact on group behavior by comparing file access policies in the context of a groupware application. © 2008 Springer Berlin Heidelberg.

Abstract

Abstract
Arguing that a system is sufficiently safe to operate in a particular context is an important element in the development of safety-critical systems. Hazard mitigation arguments support safety claims by providing evidence. They do this, typically, by appealing to barriers intended to prevent and to protect from a specific hazard. The paper summarises work on the structure of arguments, and then addresses two research questions: how understanding of the quality of arguments can be applied to hazard mitigation arguments; how making the underlying implied barrier model explicit can improve the argumentation and provide useful insights for managing risks. The EUROCONTROL Reduced Vertical Separation Minima Functional Hazard Analysis (RVSM FHA) is used to demonstrate these ideas. © 2006 Taylor & Francis Group.

Abstract
A workshop on interdisciplinary approaches to achieving and analyzing system dependability for the DSN audience is discussed. The goal of this workshop is to bring together experts from different disciplines and application domains to exchange ideas, make concrete progress across disciplinary barriers and establish contacts and possible collaborations. The selected contributions cover overlaps between the 'standard' concerns of dependable systems and networks and those of psychology, sociology and other 'human' sciences, the law, or disciplines. The format of the workshop emphasize extensive discussion and be geared to achieve effective interchange of ideas among people from different backgrounds.

Abstract
This paper describes a generic model for case memory systems expressed using the Z notation. A case memory system is an essential part of any case-based reasoning system, and provides a mechanism for storing old cases, and for assessing the relationship between the stored cases and a new problem. Using the model, characteristics that have been claimed for specific case memory systems in the literature, e.g. responsiveness to a reasoner's goals or use of past experience in case assessment, are expressed formally in terms of constraints on the means by which case relations are computed. The model supports precise reasoning about the characteristics of specific systems and offers insight into the variety of options available to software or knowledge engineers seeking to reuse a case memory system, to select a case memory system shell or to develop a new system.