Ambient Assisted Living (AAL) investigates the development of systems involving the use of different types of sensors, which monitor activities and vital signs of lonely elderly people in order to detect emergency situations or deviations from desirable medical patterns. Differently from the state-of-the-art of 'push-buttons', AAL solutions need to provide high accuracy and proactive responses, 'perceiving' lonely elderly people in their household environment through various sensors and carrying out appropriate actions under the control of the underlying software. Dependability in the AAL domain is a critical requirement, since poor system availability, reliability, safety, or integrity may cause inappropriate emergency assistance to potentially have fatal consequences. Nevertheless, contemporary research has not focused on assessing dependability in this domain. Therefore, this work aims at exploring the application of modern quantitative and qualitative dependability analysis techniques based on software architecture. The benefits of using these techniques are twofold. Firstly, they allow us to seamlessly integrate the analysis during subsequent software lifecycle stages in critical scenarios. Secondly, we aim to identify the components which have the highest impact on software system dependability, and therefore, be able to address software architecture and individual software component problems before they are implemented and critical errors occur.
Current approaches to model-driven software development have led to the use of scenarios to perform analysis of non-functional requirements of a software system in its early stages of development. The presence of implied scenarios is a phenomenon that can be observed in concurrent systems modeled in the form of Message Sequence Charts. This paper presents a methodology for the identification and evaluation of the qualitative and quantitative impact of the referred scenarios on the reliability of such systems. To the best of our knowledge, there is no previous research contribution in the literature in this regard. The applicability, as well as feasibility, of this methodology is illustrated on the example of a boiler control system. The results are then used to support the architectural refinement of the system ensuring the elimination of the undesirable implied scenarios identified and the consequent improvement in the software system reliability. The usefulness of the proposed methodology is thus confirmed to facilitate the construction of reliable concurrent software systems since the early stages of the development cycle.
I. INTRODUÇÃOA modelagem por cenários tem sido considerada uma forma eficaz de se modelar e analisar o comportamento de um sistema nos estágios iniciais do ciclo de desenvolvimento [1]. Uma das vantagens desse formatoé permitir uma participação maior dos stackholders, dado que cada cenário de uso desejadó e especificado, de acordo com essa perspectiva, utilizando o Diagrama de Sequência da UML (Unified Modeling Language)[2] ou diagramas MSCs (Message Sequence Charts) [3]. Cada cenário apresenta as trocas de mensagens entre os componentes do sistema, caracterizando sua arquitetura.São várias as abordagens que utilizam a modelagem em cenários para realizar análise de confiabilidade de software [5], [6], [7]. Entretanto, estes trabalhos, não têm até aqui, considerado nesta análise o impacto de um fenômeno denominado cenários implícitos. Cenários implícitos, que são, de forma breve, comportamentos do sistema que surgem a partir da composição paralela 1 dos componentes, cujos comportamentos são modelados nos cenários previamente especificados [8], [9]. Isso ocorre pelo fato de cenários serem visões parciais do sistema modelado, apesar de se ter em mente um comportamento global ao se modelar esses cenários. Dessa forma, quando esses cenários são integrados podem surgir novos 1 Entende-se por composição o processo de construir a arquitetura do sistema a partir do comportamento de seus componentes, utilizando para tanto métodos formais e suas técnicas de composição em paralelo [10]. comportamentos que não haviam sido anteriormente previstos [9].Esses novos cenários podem ser desejáveis, cujo efeito obtidoé aceito e integrado ao modelo, ou indesejáveis, cujo efeito gera consequências negativas, podendo levar o sistema a falhas [9]. Uma análise de confiabilidade da arquitetura realizada sobre uma modelagem em cenários que não considera esse aspecto pode levar a uma percepção equivocada do comportament...
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