Abstract
Growing software complexity is an increasing challenge for the software development of modern cyber-physical systems. A classical strategy for taming this complexity is to partition system behaviors into different operational modes specified at design time. Such a multi-mode system can change behavior by switching between modes at run-time. A complementary approach for reducing software complexity is provided by component-based software engineering (CBSE), which reduces complexity by building systems from composable, reusable and independently developed software components. CBSE and the multi-mode approach are fundamentally conflicting in that component-based development conceptually is a bottom-up approach, whereas partitioning systems into operational modes is a top-down approach with its starting point from a system-wide perspective. In this article, we show that it is possible to combine and integrate these two fundamentally conflicting approaches. The key to simultaneously benefiting from the advantages of both approaches lies in the introduction of a hierarchical mode concept that provides a conceptual linkage between the bottom-up component-based approach and system level modes. As a result, systems including modes can be developed from reusable mode-aware components. The conceptual drawback of the approach—the need for extensive message exchange between components to coordinate mode-switches—is eliminated by an algorithm that collapses the component hierarchy and thereby eliminates the need for inter-component coordination. As this algorithm is used from the design to implementation level (“compilation”), the CBSE design flexibility can be combined with efficiently implemented mode handling, thereby providing the complexity reduction of both approaches, without inducing any additional design or run-time costs. At the more specific level, this article presents (1) a mode mapping mechanism that formally specifies the mode relation between composable multi-mode components and (2) a mode transformation technique that transforms component modes to system-wide modes to achieve efficient implementation.
Highlights
Growing software complexity is posing a challenge for the design of cyber-physical systems (CPS) [1]
Based on Definition 4, we further introduce the valid local mode combination (LMC) concerning a specific mode of a composite component c, which is a feasible combination of the modes of all subcomponents of c as per the local mode mapping of c when c is running in a particular mode
We combine the advantages of both methods and propose the component-based software development of multi-mode systems, characterized by the reuse of multi-mode components, i.e., components that can run in different modes and switch mode guided by a local mode-switch manager
Summary
Growing software complexity is posing a challenge for the design of cyber-physical systems (CPS) [1]. A key issue in making such trade-offs is the risk implied by different choices; and risks have to be balanced against benefits This is a reality even for safety-critical systems regulated by safety standards. We are able to successfully integrate them in a single framework of multi-mode components, thereby providing the combined benefits of both, while being able to reduce costs to acceptable levels. These approaches, introduced below, are primarily focusing on the design, configuration and run-time phases of the system life-cycle, they do have important implications for the maintenance phase. A further implication of the enabled partitioning and inherent clearly-defined interfaces is that the approaches could scale to systems-of-systems (SoS), e.g., different components or modes can correspond to different systems in an SoS
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