Abstract: The usage of components brings significant help in development of real-time embedded systems. There have been a number of component frameworks developed for this purpose and some of them have already become well-established in this area. However, although the component frameworks share basic concepts and the general approach, they substantially differ in the range of supported features and maturity. This makes relatively difficult to select the right component framework and thus poses a significant obstacle in adoption of the component-based development for real-time embedded systems. To provide an overview, we present a survey in this paper, which illustrates distinguishing features of selected modern component-based frameworks for real-time embedded systems. The survey identifies features which are important for building systems from components in this area and compares these frameworks with respect to these features.

Abstract: We present a technique for designing reconfiguration controllers in the Fractal component-based framework. We obtain discrete control loops that automatically enforce safety properties on the interactions between components, concerning, e.g., mutual exclusions, forbidden or imposed sequences. We use a reactive programming language, with a new mechanism of behavioural contracts. Its compilation involves discrete controller synthesis, which automatically generates the correct adaptation controllers. We apply our approach to the problem of adaptive ressource management, illustrated by the example of a HTTP server.

Abstract: The composition of new applications from pre-existing parts has been one of the central notions in software reuse and component-based development for many years. Recent advances with component retrieval technologies and dynamically reconfiguring systems have brought the automated integration of components into systems into the focus of research. Even when a component offers all functionality needed by the using environment there is often a host of “syntactic obstacles” and to date there is no general solution available that can automatically address syntactic mismatches between components and their clients. In this paper we present an approach that automatically creates all syntactically feasible adapters for a given component-client constellation and selects the semantically correct one with the help of “ordinary” unit test cases. After explaining how our approach works algorithmically, we demonstrate that our prototype implementation is already able to solve a large fraction of the adaptation challenges previously identified in the literature fully automatically.

Abstract: Software systems should evolve in order to respond to changing client requirements and their evolving environments. But unfortunately, the evolution of legacy applications generates an exorbitant cost. In this paper, we propose an approach to restructure legacy object-oriented applications into component-based applications. Our approach is based on dynamic dependencies between classes to identify potential components. In this way, the composition is dictated by the context of the application to improve its evolvability. We validate our approach through the study of three legacy Java applications.

Abstract: This paper presents an architecture and implementation of a self-healing sandbox for the execution of third party code dynamically loaded which may potentially put in risk application stability. By executing code in a fault contained sandbox, no faults are propagated to the trusted part of the application. The sandbox is monitored by a control loop that is able to predict and avoid known types of faults. If the sandbox crashes or hangs, it can be automatically recovered to normal activity without needing to stop the main application. A comparison between an implementation of the sandbox in a domain-based isolation and operating-system based isolation analyses performance overhead, memory footprint and sandbox reboot time in both approaches. The implementation has been tested in a simulation of an RFID and sensor-based application.

Abstract: Dependency Resolution (DR) uses a component's explicitly declared requirements and capabilities to calculate systems where all requirements are met. DR can lead to large amounts of possible solutions because multiple versions of the same component can be available and different vendors can offer the same functionality. From this set of potential solutions DR should identify and return the optimal solution. Determining the feasibility of many optimisation techniques largely depends on the size and complexity of the DR solution search space. Using two sets of OSGi components collected from the Eclipse project and Spring Enterprise Bundle Repository, we measure the size and examine the complexity of the DR search space. By adding simple constraints based on desirable properties, we show the potentially large search space can be significantly restricted. This restriction could be used to make more complex optimisation algorithms feasible for DR.

Abstract: Design patterns are typically defined informally, albeit in a standard format, and have to be programmed by the software designer into each new application. Thus although patterns support solution reuse, in practice this does not translate into code reuse. In this paper we argue that to achieve code reuse, patterns should be defined and used in the context of software component models. We show how in such a model, behavioural patterns can be defined as composition operators which can be stored in a repository, alongside components, thus enabling code reuse.

Abstract: In the development of embedded software, modeling languages used within or across development phases e.g., requirements, specification, design, etc are based on different paradigms and an approach for relating these is needed. In this paper, we present a formal framework for relating specification and design models of embedded systems. We have chosen UML statemachines as specification models and ProCom component language for design models. While the specification is event-driven, the design is based on time triggering and data flow. To relate these abstractions, through the execution trajectories of corresponding models, formal semantics for both kinds of models and a set of inference rules are defined. The approach is applied on an autonomous truck case-study.

Abstract: In general, components provide and require services and two components are bound if the first component provides a service required by the second component. However, certain variability in services – w.r.t. how and which functionality is provided or required – cannot be described using standard interface description languages. If this variability is relevant when selecting a matching component then human interaction is required to decide which components can be bound. We propose to use feature models for making this variability explicit and (re-)enabling automatic component binding. In our approach, feature models are one part of service specifications. This enables to declaratively specify which service variant is provided by a component. By referring to a service's variation points, a component that requires a specific service can list the requirements on the desired variant. Using these specifications, a component environment can then determine if a binding of the components exists that satisfies all requirements. The prototypical environment Columbus demonstrates the feasibility of the approach.

Abstract: We present the results of an experiment investigating component collaborations in the OSGi/Eclipse component model. The aim of the experiment is to demonstrate the benefits of using a formal contract language. For this purpose, we have associated more than 1000 component collaborations in OSGi/Eclipse with formal contracts extracted from component metadata and extension point documentation. We discuss several characteristics of these contracts, including contract complexity, and verification results obtained with these contracts. To our surprise, there are numerous contract violations. This indicates that the use of a formal contract language can significantly improve the quality of dynamically composed systems.

Abstract: Many component models and frameworks have been proposed to abstract and capture concerns from Real-Time and Embedded application domains, based on high-level component-based approaches. However, these approaches tend to propose their own fixed-set abstractions and ad-hoc runtime platforms, whereas the current trend emphasizes more flexible solutions, as embedded systems must constantly integrate new functionalities, while preserving performance. In this paper, we present a two-fold contribution addressing this statement. First, we propose to express these concerns in a decoupled way from the commonly accepted structural abstractions inherent to CBSE, and provide a framework to implement them in open and extensible runtime containers. Second, we propose a three-tier approach to composition where application, containers and the underlying operating system are designed using components. Supporting a homogeneous design space allows applying optimization techniques at these three abstraction layers showing that our approach does not impact on performance. In this paper, we focus our evaluation on concerns specific to the field of real-time audio and music applications.

Abstract: With the prevalence of middleware, the amount of middleware services (abbr. services) grows increasingly large. However, an application typically utilizes a small subset of the services. In consequence, middleware is often criticized for deploying all the possible services at bootstrap. This paper advocates an on demand approach of deploying services, which is that the middleware automatically and dynamically deploys a minimal set of services according to applications' demands, so that low resource consumption, high customizability and short boot time can be obtained. By encapsulating the service as a set of independent deployable components with clearly specified dependencies, we address the problem of on demand service deployment by dint of managing dependencies among the components at runtime and propose a framework supporting the management of application, middleware components and runtime dependencies. Finally, the framework is implemented in a Java EE middleware to demonstrate its feasibility and effectiveness.

Abstract: Software engineering must cope with a more and more increasing need for evolutivity of software systems in order to make their administration easier. However, evolution and especially dynamic evolution in a system must not be done at the expense of its reliability, that is to say its ability to deliver the expected functionalities. Actually runtime modifications in a given system may lead to inconsistent states and so it can have an impact on its reliability. The aim of this paper is to guarantee reliability of dynamic reconfigurations used to make component-based systems evolve at runtime while preserving their availability. We propose a definition of consistency for configurations and reconfigurations in Fractal component architectures with a model based on integrity constraints like for example structural invariants. Reliability of reconfigurations is ensured thanks to a transactional approach which allows us both to deal with error recovery and to manage distributed and concurrent reconfigurations in Fractal applications.