Architecture Modeling - SPES 2020

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5 Using the <strong>Architecture</strong> Meta-Model 67 5.1 On the Role of Perspectives and Abstraction Layers . . . . . . . . . . . . . . . 67 5.1.1 What We Can Learn from the EDA Domain . . . . . . . . . . . . . . . 67 5.1.2 Perspectives and abstraction layers in system-level design . . . . . . . 70 5.1.3 Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 5.2 On the role of contracts in system development processes . . . . . . . . . . . . 93 5.2.1 Coping with complexity of systems . . . . . . . . . . . . . . . . . . . 93 5.2.2 Coping with the Complexity of the Supply Chain . . . . . . . . . . . . 100 5.2.3 Getting Initial Requirements Right . . . . . . . . . . . . . . . . . . . . 101 5.2.4 Coping with Multi-Layer Design Optimization . . . . . . . . . . . . . 103 5.2.5 Managing Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 5.2.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 6 Annex 108 6.1 Syntax and Semantics of RSL . . . . . . . . . . . . . . . . . . . . . . . . . . 109 6.1.1 Pattern specification . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 6.1.2 Semantics of observers . . . . . . . . . . . . . . . . . . . . . . . . . . 140 6.1.3 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 6.2 Semantics of HRC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 6.2.1 Semantical Domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 6.2.2 Properties of Trace Sets . . . . . . . . . . . . . . . . . . . . . . . . . 142 6.2.3 Semantical Definitions for HRC . . . . . . . . . . . . . . . . . . . . . 143 6.3 Syntax and Semantics of Contracts . . . . . . . . . . . . . . . . . . . . . . . . 145 6.3.1 Contract Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 6.3.2 Contracts: Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 6.4 Formalization of Typical Design Steps . . . . . . . . . . . . . . . . . . . . . . 147 Glossary 150 Bibliography 153
1 Introduction This document proposes a meta-model for architectures of embedded systems. The overall scope taken is deliberately broad, aiming at covering multiple perspectives of embeddedsystems based product development. As e. g. pointed out in [49], risk mitigation strategies in product development require a holistic approach encompassing all sub processes and their interfaces, hence requiring to cover the full range of what we call perspectives, from a geometric/physical view of the product, to a view focusing on its technical architecture, to a view elaborating its logical architecture, grouping functionality according to (sub-) system organisation, to a purely functional perspective (getting the functional specifications right), and starting with an operational perspective, focusing on interface requirements e. g. based on operational scenarios. This separation of concerns by perspectives is complemented by offering abstraction levels, as a well known principle to cope with complexity in system design. Hence design artifacts can be placed in a two-dimensional design space, organized by perspective and level of abstraction. We enrich this generic approach by a component model largely derived from the concept of Heterogeneous Rich Components (HRC)[20]. Specifically, this allows to provide rigorous interface specifications for design artifacts residing in this two-dimensional design space. The term “rich” alludes to the key ingredient of HRC components to provide (rigorous) interface specifications for multiple what we call aspects, encompassing both functional and extra-functional (e.g. safety and real-time) characteristics of components. Specifically, we propose the usage of contract-based specifications, which allow, for each aspect, to characterize the allowed design contexts of a component (through what we call strong assumptions) - violating these constitutes an out-of-specification (“illegal”) usage of the component, thus “excluding liability”: no guarantees of the component’s functional and extra-functional characteristics are given for such illegal design contexts. For allowed design contexts, the guarantee part of the contract allows to characterize both functional and extra-functional properties of the component. Often, these are case-dependent; we support what we call weak assumptions structuring contract specifications according to cases (thus refining the allowed design contexts). Weak assumptions partition the context in which the system is intended to be used with respect to its strong assumption. Hence, a single weak assumption defines only a part of the allowed system context. With this, it is possible to define different use cases for a component. If the context is able to ensure a weak assumption of a component, this component may guarantee a more restricted behavior. Note, that the notion of weak assumptions does not adress operation modes, which are switched during operation of the corresponding system. We propose a formal pattern based specification language RSL for expressing both assumptions and guarantees. RSL comes with patterns supporting multiple aspects of components; within <strong>SPES</strong> we focus on modelling functional aspects, real-time aspects, and safety aspects. We point out, that the notion of contract-based specifications is independent of the choice of the concrete formal notation for expressing contracts. Indeed, contracts can as well be formalized within other formal specification languages, such as AutoFocus [13], Live Sequence Charts [16], PSL [2], Interface Automata [22], Real-Time Statecharts [26] etc. Aspects of components can thus be rigorously specified through contracts. Their realization, 1/ 156
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Bibliography [1] ARINC 653 - Avioni
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