Author Archives: Pedro Rodrigues

Compositional Reliability Analysis for Probabilistic Component Automata

In this paper we propose a modelling formalism, Probabilistic Component Automata (PCA), as a probabilistic extension to Interface Automata to represent the probabilistic behaviour of component-based systems. The aim is to support composition of component-based models for both behaviour and non-functional properties such as reliability. We show how addi- tional primitives for modelling failure scenarios, failure handling and failure propagation, as well as other algebraic operators, can be combined with models of the system architecture to automatically construct a system model by composing models of its subcomponents. The approach is supported by the tool LTSA-PCA, an extension of LTSA, which generates a composite DTMC model. The reliability of a particular system configuration can then be automatically analysed based on the corresponding composite model using the PRISM model checker. This approach facilitates configurability and adaptation in which the software configuration of components and the associated composition of component models are changed at run time.

P. Rodrigues, E. Lupu and J. Kramer,  Compositional Reliability Analysis for Probabilistic Component Automata, to appear in International Workshop on Modelling in Software Engineering (MiSE), Florence, May 16-17, 2015.

On Re-Assembling Self-Managed Components

Self-managed systems need to adapt to changes in requirements and in operational conditions. New components or services may become available, others may become unreliable or fail. Non-functional aspects, such as reliability or other quality-of- service parameters usually drive the selection of new architectural configurations. However, in existing approaches, the link between non-functional aspects and software models is established through manual annotations that require human intervention on each re-configuration and adaptation is enacted through fixed rules that require anticipation of all possible changes. We propose here a methodology to automatically re-assemble services and component-based applications to preserve their reliability. To achieve this we define architectural and behavioural models that are composable, account for non-functional aspects and correspond closely to the implementation. Our approach enables autonomous components to locally adapt and control their inter- nal configuration whilst exposing interface models to upstream components.

P. Rodrigues, J. Kramer and E. Lupu,  On Re-Assembling Self-Managed Components, to appear in International Symposium on Integrated Network and Service Management (IM), Ottawa, May 11-15, 2015

LTSA-PCA : Tool support for compositional reliability analysis

ltsa-pca-pic

Software systems are constructed by combining new and existing services and components. Models that represent an aspect of a system should therefore be compositional to facilitate reusability and automated construction from the representation of each part. In this paper we present an extension to the LTSA tool  that provides support for the specification, visualisation and analysis of composable probabilistic behaviour of a component-based system using Probabilistic Component Automata (PCA). These also include the ability to specify failure scenarios and failure handling behaviour. Following composition, a PCA that has full probabilistic information can be translated to a DTMC model for reliability analysis in PRISM. Before composition, each component can be reduced to its interface behaviour in order to mitigate state explosion associated with composite representations, which can significantly reduce the time to analyse the reliability of a system. Moreover, existing behavioural analysis tools in LTSA can also be applied to PCA representations.