Multi-Paradigm Modelling Approaches for Cyber-Physical Systems

Multi-Paradigm Modelling for Cyber-Physical Systems explores modeling and analysis as crucial activities in the development of Cyber-Physical Systems, which are inherently cross-disciplinary in nature and require distinct modeling techniques related to different disciplines, as well as a common background knowledge. This book will serve as a reference for anyone starting in the field of CPS who needs a solid foundation of modeling, including a comprehensive introduction to existing techniques and a clear explanation of their advantages and limitations. This book is aimed at both researchers and practitioners who are interested in various modeling paradigms across computer science and engineering.

• Identifies key problems and offers solution approaches as well as tools which have been developed or are necessary for modeling paradigms across cyber physical systems
• Explores basic theory and current research topics, related challenges, and research directions for multi-paradigm modeling
• Provides a complete, conceptual overview and framework of the research done by the MPM4CPS working groups and the different types of modeling paradigms developed

• Language: English
• Publisher: Academic Press
• Release date: Nov 20, 2020
• ISBN: 9780128191064

Book preview

Chapter 1: Introduction

Bedir Tekinerdogana; Dominique Blouinb; Hans Vangheluwec; Miguel Goulãod; Paulo Carreirad; Vasco Amarald    aWageningen University & Research, Wageningen, The Netherlands

bTelecom Paris, Institut Polytechnique de Paris, Paris, France

cUniversity of Antwerp and Flanders Make, Antwerp, Belgium

dUniversity of Lisbon, Lisbon, Portugal

Abstract

This introductory chapter provides the context and the motivation for multi-paradigm modeling for cyber-physical systems (MPM4CPS). Three basic parts are presented, including an ontological framework for MPM4CPS, methods and tools, and case studies.

Keywords

Multi-paradigm modelling; cyber-physical systems; ontology; case studies

1.1 Objectives

Truly complex, multidisciplinary, engineered systems, known as Cyber-Physical Systems (CPSs), are emerging in today's reality. Those integrate physical, software, and network aspects in a sometimes adverse physical environment. We can find examples of CPSs in autonomous cars, industrial control systems, robotics systems, medical monitoring, and automatic pilot avionics, to name a few. The cover of the book, for instance, shows another example of a complex CPS, the Maltese Falcon sailing yacht, one of the world's most complex and largest yachts. The act of sailing consists of employing the wind, acting on sails, propelling the craft on the surface of the water in the most different environment scenarios (the Sea conditions can be somewhat unpredictable). Operation of these crafts, with speed and fuel-saving concerns, is traditionally done by skilled skippers and can be appreciated as a sport. Here, like in other sports such as Formula-1, automation stepped into the design, simulation to support the decision and optimise, and operation in both stationary and unsteady conditions. Here, besides the several degrees of freedom of motion, a complex dynamic of forces must be controlled by balancing hydrodynamics, aerodynamics, buoyant and gravitational forces.

As Maltese Falcon, to build such boats is a complicated engineering endeavour with challenging technological and physical constraints (with impact in the used materials, communications, etc.). Maltese Falcon has 88 meters long (289 feet) and can be operated by a single person. To do that, she counts with a wide plethora of actuating devices, including freestanding rotating masts. Also, to support a complex control logic, there is a complex set of sensors with advanced technology such as fiber optical strain net into the spars to analyse real-time loads under sail. The yacht's sophisticated computer software can automatically detect parameters such as wind speed and display critical data to the operator. This autonomy property is characteristic of many CPSs.

Despite the increased adoption and impact of CPSs (where Maltese Falcon is an example), no unifying theory nor systematic design methods, techniques, and tools exist for such systems. Individual (mechanical, electrical, network, or software) engineering disciplines only offer partial solutions. Multi-Paradigm Modelling (MPM) proposes to model every part and aspect of a system explicitly, at the most appropriate level(s) of abstraction, using the most appropriate modelling formalism(s). Modelling languages engineering, including model transformation, and the study of their semantics, are used to realise MPM. MPM is seen as an effective answer to the challenges of designing CPS.

Modelling and analysis are crucial activities in the development of Cyber-Physical Systems. Moreover, the inherent cross-disciplinary nature of CPS requires distinct modelling techniques related to different disciplines to be employed. At the same time, to enable communication between all specialities, common background knowledge is needed.

Anyone starting in the field of CPS will be faced with the need for literature with solid foundations of modelling CPS and with a comprehensive introduction to the distinct existing techniques with clear reasoning on their advantages and limitations. Indeed, although most of these techniques are already used as a matter of common practice in specific disciplines, the knowledge of their fundamentals and application is typically far away from practitioners of another area. The net result is the tendency for CPS practitioners to use the technique that they are most comfortable with, disregarding the technique that would be the most adequate for the problem and modelling goal.

This book is the result of cooperation made possible by the COST Action IC1404 Multi-Paradigm Modelling for Cyber-Physical Systems (MPM4CPS), which allowed researchers, institutions and companies from 32 countries to collaborate over four years.

The goal of this book is to serve as a showcase of the research outcomes of the different workgroups of the MPM4CPS network. As such, the book is expected to cover the results on the foundations, formalisms, tools, and educational resources produced within the MPM4CPS network (e.g., case studies made available by the MPM4CPS network). The text will focus on state-of-the-art research and practice knowledge.

The book includes both chapters that discuss experiences from the industry and papers that are more research-oriented. Practitioners will benefit from the book by identifying the critical problems, the solution approaches, and the tools that have been developed or are necessary for model management and analytics. Researchers will benefit from the book by identifying the underlying theory and background, the current research topics, the related challenges, and the research directions for the model management and analytics. The book will also help graduate students, researchers, and practitioners to get acquainted with recent research outcomes of the MPM4CPS network.

1.2 Outline of the book

The book consists of three basic parts: an ontological framework for MPM4CPS; methods and tools; and, finally, case studies. Part 1 provides the ontological framework for MPM4CPS and includes Chapter 2 to Chapter 5. The ontology framework is decomposed into four sub-parts: a shared ontology to capture concepts that are needed by the other ontologies but that do not pertain to their domains, an ontology for CPS, an ontology for MPM and an integrated ontology for MPM4CPS. For deriving the ontologies, a thorough domain analysis process has been carried out that has focused on key selected primary studies on MPM4CPS. Part 2 describes the methods and tools that are used to develop and analyse CPSs. Chapter 6 to Chapter 9 cover these topics. Part 3 of the book considers case studies which are addressed in Chapter 10 and Chapter 11.

1.2.1 Part 1 – Ontological framework

Chapter 2 introduces the modelling approach and tools that have been chosen to define the ontology, to both motivate and clarify the methods and the actual directions that led the research effort. It also provides a description of the shared ontology whose concepts are used to frame in a more general context some of the more specific notions of the other ontologies. Then, the chapter presents a brief description of the examples we adopted as references to start exploring the field, to glance at our vision of the domain and to guide the reader through our exploration path.

The ontology for CPS is described in Chapter 3. Hereby, a feature modelling approach is adopted that explicitly models the common and variant features of a CPS. Each feature of the resulting feature model is described in detail. The resulting feature model shows the configuration space for developing CPSs. The two case studies on CPS that were introduced in Chapter 2 are used to derive the concrete CPS configurations.

Chapter 4 presents the ontology for MPM specified using the Web Ontology Language (OWL). The chapter first presents a thorough state-of-the-art treatment of MPM's core notions, multi-formalism and model management approaches, languages, and tools, which is an essential component to support MPM. Model management approaches are characterised according to their modularity and incremental execution properties as required to scale for the large complex systems we face today. Subsequently, an overview of the MPM ontology is developed, including the main classes and properties of the ontology. Usage of the MPM ontology is illustrated for the two case studies introduced in Chapter 2.

Chapter 5 integrates the results of the previous chapters by presenting an integrated ontology for MPM4CPS. Hereby, the chapter also elaborates on and integrates the Shared, CPS, and MPM ontologies by providing cross-cutting concepts between these domains. It formalises notions such as model-based development processes, their employed viewpoints supported by megamodel fragments and the CPS parts under development covered by these viewpoints. It finally introduces some ongoing work at the heart of MPM4CPS on the formalisation of modelling paradigm notions in the more general context of engineering paradigms.

1.2.2 Part 2 – Methods and tools

Chapter 6 presents the two-hemisphere model-driven (2HMD) approach for enabling the composition of CPSs. The approach assumes modelling and the use of procedural and conceptual knowledge on an equal and interrelated basis. This differentiates the 2HMD approach from pure procedural, purely conceptual, and object-oriented approaches. This approach may be applied in the context of modelling of a particular business domain as well as in the context of modelling the knowledge about the domain. Cyber-physical systems are heterogeneous systems that require a multi-disciplinary approach for their modelling. Modelling of cyber-physical systems by the 2HMD approach gives an opportunity to compose and analyse system components to be provided transparently and components actually provided, thus identifying and filling the gap between desirable and actual system content.

In Chapter 7, the authors illustrate how a co-simulation technology can be used to gradually increase the details in a collaborative model (co-model) following a discrete event first" (DE-first) methodology. In this approach, initial abstract models are produced using a discrete event (DE) formalism (in this case, VDM) to identify the proper communication interfaces and interaction protocols among different models. These are gradually replaced by more detailed models using appropriate formalisms, for example, continuous-time (CT) models of physical phenomena.

Chapter 8 presents an agent-based CPS development approach using a domain-specific modelling language, SEA ML++. The paper elaborates on intelligent agents, which are software components that can work autonomously and proactively to solve the problems collaboratively. Agents can behave in a cooperative manner and collaborate with other agents constituting systems called Multi-agent Systems (MAS). Intelligent software agents and MASs can be used in the modelling and development of CPSs. In this chapter, the authors discuss how SEA ML++ is used for the design and implementation of agent-based CPSs. An MDE methodology is introduced in which SEA ML++ can be used to design agent-based CPS and implement these systems on various agent execution platforms. As evaluating case study, the development of a multi-agent garbage collection CPS is taken into consideration. The conducted study demonstrates how this CPS can be designed according to the various viewpoints of SEA ML++ and then implemented on JASON agent execution platform.

Chapter 9 focuses on hybrid systems modelling, which is essential for CPS. The expressiveness for hybrid systems modelling allows for the definition of highly complex systems that merge discrete state-based transitions systems with continuous value-evolutions for variables. That way, cyber-physical systems can be modelled in all their intricacies. However, this expressive power comes at a downside of complex models and undecidable verification problems even for small systems. In this chapter, the authors present CREST, a novel modelling language for the definition of hybrid systems. CREST merges features from various formalisms and languages such as hybrid automata, data flow programming, and internal DSL designs to create a simple yet powerful language for modelling resource flows within small-scale CPS such as automated gardening applications and smart homes. The language provides an easy-to-learn graphical interface and is supported by a Python-based tool implementation that allows the efficient modelling, simulation, and verification of CPS models.

1.2.3 Part 3 – Case studies

Chapter 10 describes the design and development of an IoT- and WSN-based CPS using MPM Approach for a Smart Fire Detection Case Study. The system is developed using the Internet of Things (IoT) components and Wireless Sensor Network (WSN) elements. The proposed system is composed of different hardware parts, software elements, computing components, and communication technologies, resulting in a complex system considering both its structure and behaviour. The chapter elaborates on different phases of the development process, including requirement analysis, design, modelling and simulation, and implementation. To present the MPM approach during these phases, the Formalism Transformation Graph and Process Model (FTG+PM) is utilised, and all the involved artifacts and model transformations are described. This helps to provide the data flow and the control flow of the system development in the PM. Further, the analysis of the FTG shows the possible improvements for the system by finding the critical manual transformation to be (semi-)automated.

Chapter 11 presents the development of industry-oriented cross-domain study programs in CPSs for Belarussian and Ukrainian Universities. The paper aligns with the targets of the European COST Action MPM4CPS project, which also considered the dissemination of the results in the educational context. The chapter presents the process and results for creating the base for a European Master and Ph.D. program in MPM4CPS involving European Leading Universities. Further, it elaborates on setting up the respective discipline road-map facing the challenge to develop a mutually recognised cross-domain expertise-based study program in CPS. One of the challenges in the development of study programs is bridging the gap between industry needs and educational output, in terms of training the prospective researchers and engineers in the CPS field. The success of MPM4CPS encouraged EU partners to apply knowledge and methods, developed by the COST Action at an ERASMUS+ project, to validate in practice its viability aiming to develop the industry-focused curricula at the partners' universities of Belarus and Ukraine. The chapter discusses how the COST team efforts towards an analysis of tendencies, industry needs, and acquiring best education practices have been applied by the ERASMUS+ team to create industry-focused cross-domain study programs in CPS for the partners' universities of Belarus and Ukraine.

1.3 Acknowledgements

This book was supported by the COST Action IC1404 Multi-Paradigm Modelling for Cyber-Physical Systems (MPM4CPS), COST is supported by the EU Framework Programme Horizon 2020.

INESC-ID authors were supported by national funds through FCT (Fundação para a Ciência e a Tecnologia) under contract UID/CEC/50021/2019. Also, NOVA authors were supported by NOVA LINCS Research Laboratory y (Ref. UID/CEC/04516/2019) and bilateral project Portugal-Germany, Modelação de Sistemas Sócio Ciberfísicos, Proc. 441.00 DAAD.

Telecom Paris authors were partially supported by the US Army Research, Development and Engineering Command (RDECOM).

Finally, we would like to thank all the authors and contributors of the chapters.

Part 1: Ontological framework

Outline

Chapter 2. An ontological foundation for multi-paradigm modelling for cyber-physical systems

Chapter 3. A feature-based ontology for cyber-physical systems

Chapter 4. An ontology for multi-paradigm modelling

Chapter 5. An integrated ontology for multi-paradigm modelling for cyber-physical systems

Chapter 2: An ontological foundation for multi-paradigm modelling for cyber-physical systems

Dominique Blouina; Rima Al-Alib; Mauro Iaconoc; Bedir Tekinerdogand; Holger Giesee    aTelecom Paris, Institut Polytechnique de Paris, Paris, France

bCharles University, Prague, Czech Republic

cUniversity of Campania Luigi Vanvitelli, Caserta, Italy

dWageningen University & Research, Wageningen, The Netherlands

eHasso-Plattner-Institut, Potsdam, Germany

Abstract

This chapter introduces the different background material needed to understand the next three Chapters respectively presenting the Cyber-Physical Systems (CPS), Multi-Paradigm Modelling (MPM) and Multi-Paradigm Modelling for Cyber-Physical Systems (MPM4CPS) ontologies. It first introduces the approach and tools that have been used to define the ontologies. It then provides an overview of the ontological framework and a description of the shared ontology, which provides concepts defined in order to frame in a more general context some of the more specific notions of the other ontologies. Then, the chapter presents a brief introduction of the two CPS engineering environments employing MPM that were used to explore the domains covered by the ontologies and to guide readers through our exploration path.

Keywords

Cyber-physical systems; multi-paradigm modelling; ontology; OWL; feature modelling; Protégé

2.1 Introduction

The domain of Cyber-Physical Systems (CPSs) arises from the natural technological evolution of control systems, the increased reliability and speed of modern networks and the possibility of obtaining sophisticated coordination, supervision and control of complex, possibly distributed and interacting systems by means of software. CPS conjugate in a single system a computer-based (cyber) part, characterised by discrete time behaviour and isolation from the physical world when non interacting, dominated by software and by algorithmic descriptions, and a physical part, operating in the real, continuous time and in the concrete, tridimensional space, without isolation from the external world and dominated by kinematics, dynamics and all possible undesired influences of natural phenomena.

The complementarity between the two components may allow a prompt management of the physical one by means of a reactive context management and a proper drive of actuators, given an appropriate sensorisation of the physical component: the cyber component may provide unprecedented intelligence, beyond any previous conventional possibility, to the system, assuming that proper design techniques are available to think and develop it as a whole.

Developing an appropriate design technique is very challenging. Variety in components, diversity in specification, criticality in requirements, heterogeneity in the time structure behind the cyber and the physical components and interdependence between different aspects and specifications for the overall system and for its components make the complexity of the design process manageable only if the conceptual approach can encompass every specific aspect of each part of the system while keeping internal coherence in front of modification in the design choices for a component or a subsystem. In fact, as different paradigms coexist in CPS, an appropriate design technique must be aware of the involved paradigms, and actually leverage them to encompass the nature of each component by bending the design process to embrace the most natural modelling paradigm at components level and at each abstraction level in which the overall system can be observed to cope with specific aspects of the general problem.

On these premises, we present in this book parts of the results of a wide cooperative research effort that has proposed Multi Paradigm Modelling (MPM) as a key approach to provide a sound foundation for design processes targeting CPS. MPM supports the coordinated use of different modelling paradigms, model transformation techniques, compositional modelling approaches to shape the target system starting from the specification phase to the validation phase of the design cycle, leveraging different modelling techniques and approaches to evolve the design through models suitable for all the needs that design implies, including the satisfaction of non-functional specifications, such as correctness and performances, and their evaluation from the earliest phases of the design and development process. A MPM approach exploits different tools, different frameworks, different mathematical or formal foundations: consequently, the definition of such an approach suitable for CPS requires a careful exploration of the state of the art of modelling techniques and tools to understand how they are structured, which purposes they serve, what goals they intend to achieve, how they allow one to achieve the goals, and the definition of a common framework for the integration of the semantics they use to describe models, results, syntactic aspects, evaluation or generation or transformation processes. Such an exploration led to an ontology-based description of the domains of MPM, CPS and MPM4CPS, in order to map MPM concepts to the CPS domain and to understand how MPM approaches should be shaped to better fit the needs of a CPS design process.

This chapter introduces the modelling approach that has been chosen to define the ontology, in order to both motivate and clarify the methods and the actual directions that led the research effort. Readers will also find a presentation of the overall architecture of the ontological framework, divided into four ontologies including a shared ontology to capture concepts that are needed by the other ontologies but that do not pertain to their domains. This shared ontology is also presented as it supports the other ontologies of the other chapters. Then a brief description of the examples we adopted as references to start exploring the field is presented, in order to provide a glance on our vision of the domain and to guide the reader through our exploration path.

The next chapters will then present in detail our ontology for CPS, to give a precise connotation of what our design target looks like, our ontology for MPM, to present the results of our analysis and provide the reader with a comprehensive knowledge of the state of the art of contemporary modelling culture, and the integration between the two, which is the final result of our work.

The cooperation behind these results has been made possible by the COST Action IC1404 Multi-Paradigm Modelling for Cyber-Physical Systems (MPM4CPS), which allowed the collaboration of researchers, institutions and companies from 32 countries over 4 years.

2.2 Ontology development approach

This section presents the approach we have followed for the development of our ontological framework. It required one to analyse the domains of CPS, MPM and their joint use for the development of CPS with MPM as the MPM4CPS integrated domain. The workflow for the ontology development approach is shown in Fig. 2.1.

Figure 2.1 Ontology development approach.

Developing these ontologies was performed following an exploratory modelling mode supporting our domain analysis process. Therefore in the following section we briefly introduce this modelling mode. Then we present the followed domain analysis process and finally we introduce the two concrete modelling formalism and tools that were used to capture the domains.

2.2.1 Modelling modes

According to [1], modelling can be categorised into exploratory and constructive modes each following a different school of thought. Each mode has a different goal with different characteristics employed in order to achieve the goal. Such characteristics are listed in Table 2.1.

Table 2.1

Exploratory modelling aims at understanding a domain problem by providing a description for it, often in the form of a classification. It typically makes use of a bottom-up approach where instances of the domain are studied and typed according to their structure (properties). It therefore assumes an open world where not all types are known in advance, but are rather discovered as new instances are classified. It typically uses modelling languages such as the Web Ontology Language¹ (OWL) to specify the classification and Description Logic (DL) to reason about it.

Conversely, Constructive modelling aims at building solutions for a domain by prescribing nominal types for all elements of the domain. It therefore assumes a closed world following a top-down approach where all types of instances are known via an instantiation relation. It uses nominal typing and is supported by modelling languages such as UML and first-order logic via constraint languages such as OCL.

Given the objective of this work, both of these modelling modes are actually needed. It is well known that a sound understanding of a problem to be solved is a prerequisite for building a good solution to the problem. Therefore, a solid understanding of existing CPSs and the way they are developed with models is required to develop a solution to properly relate / combine modelling languages and techniques for CPS development, which was the objective of working group 1 of the MPM4CPS COST action.

In this work, however, we are only concerned with the first phase; exploratory modelling. The objective is that the developed classification of the ontological framework can later serve as a basis to engineer a model management framework using constructive modelling in order to properly Relate / Combine Modelling Languages and Techniques for CPS development. Therefore, this first part of this book on foundations of MPM4CPS is dedicated to presenting the developed MPM4CPS ontologies and the next constructive modelling step is left as future