%&tex
\chapter{Introduction}
\label{introduction}
\section{Context of this Thesis}
    \ac{cps} are computer systems which control and monitor a physical system.
    This physical system is often a system of mechanical components which are deeply intertwined with the software components.
    Automobiles, robots, medical devices and even the smart grid are examples of \ac{cps}.
    The complexity of \ac{cps} has gone from an embedded system that improved the fuel consumption of a car engine to a fully self-driving vehicle.
    Although the complexity opens up more design possibilities, improved efficiency, and beter safety, it has downsides.
    The problem with the increasing complexity is the resulting increased developing cost and the decreasing reliability.
    Within the research topics that focus on \ac{cps}, lies the development of new design methods that deal with this complexity problem.
    The \emph{design method} by \textcite{broenink_rapid_2019} is one of these new design methods and focusses on the rapid development of embedded control software.
    The rapid development is a design technique that splits the development into small individual steps, which are implemented and tested separately.
    Testing each individual step creates feedback on a short interval, with the goal to detect errors made during the development as early as possible.
    As part of the research, Broenink and Broenink performed a small case study.
    In this case study, they have designed a controller, and implemented the controller in software for a physical off-the-shelf system.
    However, developing \ac{cps} incorporates both the computational software side, as well as the development of the physical dynamic side, although the latter is not covered by Broenink and Broenink.
    For this design method to be suitable for a complete design of \ac{cps} it has to be applicable to the physical part as well.
    
    %%In this thesis, the proposed design method is applied and evaluated in the context of the physical part of a \ac{cps}.
    %%This is done in a case study, where a \ac{cps} is designed from scratch.
\section{Research Objective}
    \textcite{broenink_rapid_2019} present a case study for software in their paper and state that "this [case study] does not mean that the same techniques cannot be applied to the physical part of the system."
    In this thesis, I will research whether this design method applies to the physical part of a \ac{cps}, to come to a design method that can be applied on both the physical and cyber (software) part of a \ac{cps}.
    From the start of this research, it was clear that a direct copy of the design method is not possible.
    It is therefore necessary to analyse which design techniques cannot be used and thus how to replace or improve them.
    The research is summarized in the following two research questions:
    \begin{itemize}
        \item Which design techniques of the design method by \textcite{broenink_rapid_2019} can be applied developing the physical part of \ac{cps}?
        \item Which adaptations are required to make the design method by \textcite{broenink_rapid_2019} suitable for developing the computation and physical part of \ac{cps}?
    \end{itemize}

\section{Approach}
    Within this thesis, the design method by \textcite{broenink_rapid_2019} is evaluated in a case study.
    The case study performs a development process according to the design method and evaluates the result.
    However, there are a couple of steps required prior to the start of the case study (see \autoref{fig:approach}).
    The first step is to produce a concrete \emph{design plan} based on the design method.
    The concrete design plan improves the evaluation of the design techniques.
    The design method is presented in an abstract form which leaves room for interpretation.
    This hampers the evaluation process, because it is impossible to point out flaws in something that was not specific in the first place.
    Therefore, I will assess the design method and add detail to get a concrete design plan.
    Because the design method focusses on the rapid development principles and modelling techniques, it does not cover the design steps outside of that focus.
    These steps, like problem definition and system specifications, are a crucial part of the design process and are added to create the concrete design plan.
    The added steps are based on the steps in a \ac{se} approach.
    \begin{figure}
        \centering
        \includegraphics[width=9cm]{graphics/approach.pdf}
        \caption{A graph that shows the interconnection of the different steps that are required to prior to the start of the case study.}
        \label{fig:approach}
    \end{figure}

    With a design plan to use in the case study there are two steps of preparation left.
    The first step is to develop an evaluation plan to ensure complete and consistent feedback during the case study.
    The evaluation plan consists of a list of questions that have to be evaluated for each design step.
    There are specific questions that evaluate the definition, or the execution of the design step.
    The other step is to provide the \emph{subject of design} to develop in the case study.
    Normally, the design process focusses on delivering the end product in the most effective manner.
    However, the goal of this research is to use the design process to evaluate the design method, not to develop a product.
    A possible pitfall is that during the design process a simple solution is found, such that the design techniques to deal with the increased complexity are left untouched.
    Choosing to develop a very complex subject ensures that the case study covers all the design techniques.
    Unfortunately, the limited time budget of a master's thesis makes it impossible to perform a case study for a complex subject.
    One of the requirements for the possible subjects is therefore a minimum level of complexity, forcing the developer to not go with the simplest solution.
    Some other requirements, based on practical decisions like budget, tools, and time were defined as well.
    Based on these requirements, the subject of choice is "Writing a tweet on a whiteboard".
    
    With something to develop, a method to develop, and a method to evaluate, the case study is executed.
    Even though the case study was terminated due to the limited amount of time available, it resulted in a partial prototype of a whiteboard writer and a significant amount of evaluation.
    The results made it possible to propose improvements to the design method, not only for the physical part of \ac{cps} but also the cyber part.

\section{Notes on Terminology}
    Design method is a commonly-used notion throughout the different papers and research used in this thesis.
    \textcite{broenink_rapid_2019} refer to their design method as 'the methodology', which is to generic for this thesis.
    To ensure distinct terminology throughout this thesis, their methodology is named \acl{ridm} and is abbreviated as \acs{ridm}.
    The more concrete version of the design method that is tested in the case study, is referred to as the 'design plan'.
    The object or system that is going to be designed during the case study is referred as 'subject of design'.

\section{Structure}
    The refinement of the design method and adding design steps is done in \autoref{analysis} to define a concrete design plan.
    The evaluation plan and subject of design is defined in \autoref{case_method}.
    The case study is executed in \autoref{case_experiment}, based on the design plan, evaluation plan and subject of design.
    The execution of the case study is evaluated in \autoref{case_evaluation}.
    In \autoref{reflection} the evaluation of the case study and the results are reflected back on the design plan.
    Based on the reflection and the evaluation, an improved design method is proposed in \autoref{improved_design}.
    And finally, the research is concluded in \autoref{conclusion}.
