Genaína Nunes Rodrigues

Using scenarios to predict the reliability of concurrent component-based software systems

Scenarios are a popular means for capturing behavioural requirements of software systems early in the lifecycle. Scenarios show how components interact to provide system level functionality. If component reliability information is available, scenarios can be used to perform early system reliability assessment. In this paper we present a novel automated approach for predicting software system reliability. The approach involves extending a scenario specification to model (1) the probability of component failure, and (2) scenario transition probabilities derived from an operational profile of the system. From the extended scenario specification, probabilistic behaviour models are synthesized for each component and are then composed in parallel into a model for the system. Finally, a user-oriented reliability model described by Cheung is used to compute a reliability prediction from the system behaviour model. The contribution of this paper is a reliability prediction technique that takes into account the component structure exhibited in the scenarios and the concurrent nature of component-based systems. We also show how implied scenarios induced by the component structure and system behaviour described in the scenarios can be used to evolve the reliability prediction.

Reliability prediction in model-driven development

Evaluating the implications of an architecture design early in the software development lifecycle is important in order to reduce costs of development. Reliability is an important concern with regard to the correct delivery of software system service. Recently, the UML Profile for Modeling Quality of Service has defined a set of UML extensions to represent dependability concerns (including reliability) and other non-functional requirements in early stages of the software development lifecycle. Our research has shown that these extensions are not comprehensive enough to support reliability analysis for model-driven software engineering, because the description of reliability characteristics in this profile lacks support for certain dynamic aspects that are essential in modeling reliability. In this work, we define a profile for reliability analysis by extending the UML 2.0 specification to support reliability prediction based on scenario specifications. A UML model specified using the profile is translated to a labelled transition system (LTS), which is used for automated reliability prediction and identification of implied scenarios; the results of this analysis are then fed back to the UML model. The result is a comprehensive framework for addressing software reliability modeling, including analysis and evolution of reliability predictions. We exemplify our approach using the Boiler System used in previous work and demonstrate how reliability analysis results can be integrated into UML models.

A model driven approach for software systems reliability

The main contribution of this research is to provide platform-independent means to support reliability design following the principles of a model driven approach. The contribution aims to systematically address dependability concerns from the early to the late stages of software development. MDA appears to be a suitable framework to assess these concerns and, therefore, semantically integrate analysis and design models into one environment.

Sensitivity analysis for a scenario-based reliability prediction model

As a popular means for capturing behavioural requirements, scenarios show how components interact to provide system-level functionality. If component reliability information is available, scenarios can be used to perform early system reliability assessment. In previous work we presented an automated approach for predicting software system reliability that extends a scenario specification to model (1) the probability of component failure, and (2) scenario transition probabilities. Probabilistic behaviour models of the system are then synthesized from the extended scenario specification. From the system behaviour model, reliability prediction can be computed. This paper complements our previous work and presents a sensitivity analysis that supports reasoning about how component reliability and usage profiles impact on the overall system reliability. For this purpose, we present how the system reliability varies as a function of the components reliabilities and the scenario transition probabilities. Taking into account the concurrent nature of component-based software systems, we also analyse the effect of implied scenarios prevention into the sensitivity analysis of our reliability prediction technique.

Reliability Analysis of Concurrent Systems Using LTSA

In this paper, we present an extension of LTSA that facilitates our approach to reliability prediction. LTSA allows the use of behavioural models for distributed systems as prototypes to explore system behaviour, and automated checking of model compliance to properties (i.e., model checking). To support reliability prediction, our new extensions allow annotating a scenario specification with probabilities and using LTSA to process the resulting scenarios. In this context, scenarios are partial descriptions of how components interact to provide system functionality. A scenario specification is formed by composing multiple scenarios possibly from different stakeholders.