Paulo Asterio de Castro Guerra

A fault-tolerant software architecture for component-based systems

Component-based software built from reusable software components is being used in a wide range of applications that have high dependability requirements. In order to achieve the required levels of dependability, it is necessary to incorporate into these complex systems means for coping with software faults. However, the problem is exacerbated if we consider the current trend of integrating off-the-shelf software components, from independent sources, which allow neither code inspection nor changes. To leverage the dependability properties of these systems, we need solutions at the architectural level that are able to guide the structuring of unreliable components into a fault-tolerant architecture. In this paper, we present an approach for structuring fault-tolerant component-based systems based on the C2 architectural style.

A Dependable Architecture for COTS-Based Software Systems Using Protective Wrappers

Commercial off-the-shelf (COTS) software components are built to be used as black boxes that cannot be modified. The specific context in which these COTS components are employed is not known to their developers. When integrating such COTS components into systems, which have high dependability requirements, there may be mismatches between the failure assumptions of these components and the rest of the system. For resolving these mismatches, system integrators must rely on techniques that are external to the COTS software components. In this paper, we combine the concepts of an idealised architectural component and protective wrappers to develop an architectural solution that provides an effective and systematic way for building dependable software systems from COTS software components.

A systematic approach for structuring exception handling in robust component-based software

Component-based development (CBD) is recognized today as the standard paradigm for structuring large software systems. However, the most popular component models and component-based development processes provide little guidance on how to systematically incorporate exception handling into component-based systems. The problem of how to employ language-level exception handling mechanisms to introduce redundancy in componentbased systems is recognized by CBD practitioners as very difficult and often not adequately solved. As a consequence, the implementation of the redundant exceptional behaviour causes a negative impact, instead of a positive one, on system and maintainability. In this paper, we propose an approach for the construction of dependable component-based systems that integrates two complementary strategies: (i) a global exception handling strategy for inter-component composition and (ii) a local exception handling strategy for dealing with errors in reusable components. A case study illustrates the application of our approach to a real software system.

An Architectural-Level Exception-Handling System for Component-Based Applications

Component-based software systems built out of reusable software components are being used in a wide range of applications which have high dependability requirements. In order to accomplish the required levels of dependability, it is necessary to incorporate into these complex systems means for to cope with software faults. Exception handling is a well-known technique for adding forward error recovery to software systems supported by various mainstream programming languages. However, exception handling for component-based applications at the architectural level introduces new challenges which are not addressed by traditional exception handling systems, such as unavailability of source code, specially when off-the-shelf components are employed. In this paper, we present an exception handling system which adds fault tolerance to component-based systems at the architectural level. Our solution considers issues which are specific to component-based applications, such as unavailability of source code. We also present a framework which implements the proposed exception handling system for applications built using the C2 architectural style.

A fault-tolerant software architecture for COTS-based software systems

This paper considers the problem of integrating Commercial off-the-shelf (COTS) components into systems with high dependability requirements. Such components are built to be reused as black boxes that cannot be modified. The system architect has to rely on techniques that are external to the component for resolving mismatches between the services required and provided that might arise in the interaction of the component and its environment. The paper puts forward an approach that employs the layer-based C2 architectural style for structuring error detection and recovery mechanisms to be added to the component during system integration.

Structuring exception handling for dependable component-based software systems

Component-based development (CBD) is recognized today as the standard paradigm for structuring large software systems. However, the most popular component models, such as Enterprise Javabeans and DCOM, provide almost no guidance about how to incorporate exception handling into component-based systems. The problem of how to employ language-level exception handling mechanisms to incorporate fault-tolerance in component-based systems is recognized by CBD practitioners as very difficult and often not adequately solved, with negative impact on reliability and maintainability. We believe that the construction of dependable component-based systems requires both (i) a global exception handling strategy for inter-component composition and (ii) a local exception handling strategy for dealing with errors within the reusable components. In This work we describe a general strategy for the development of fault-tolerant software components and their integration into dependable component-based software systems.

Software architectures for dependable systems

Although there is a large body of research in dependability, architectural level reasoning about dependability is only just emerging as an important theme in software development. This is due to the fact that dependability concerns are often left until too late in the process of development. In addition, the complexity of emerging applications and the trend of building trustworthy systems from existing untrustworthy components are urging dependability concerns to be considered at the architectural level.