\begin{document}
\chapter{Prelude}%
\label{chp:introduction}
-In 2022, there were an estimated number of 13.4 billion of connected computers that sense, act or otherwise interact with people, other computers and the physical world surrounding us\footnote{\url{https://transformainsights.com/research/tam/market}, accessed on: \formatdate{13}{10}{2022}}.
-The variety among these devices is considerable but these devices have one thing in common though: they are all controlled by software.
-Concretely this means that programmers write code for these specific device to make sure the brains of the device---the processor---do what we want it to do.
+\begin{chapterabstract}
+ This chapter introduces the contents of the thesis and a reading guide.
+ Furthermore, it provides background material on \glsxtrlong{IOT}, \glsxtrlongpl{DSL}, and \glsxtrlong{TOP}; and a detailed overview of the contributions.
+\end{chapterabstract}
+
+There are at least 13.4 billion computers connected to the internet at the time of writing\footnote{\url{https://transformainsights.com/research/tam/market}, accessed on: \formatdate{13}{10}{2022}}.
+These devices sense, act, or otherwise interact with people, other computers, and the world surrounding us.
+Notwithstanding the substantial variety among these devices, they have one thing in common: they are all require software to operate.
An increasing amount of these connected devices are so-called \emph{edge devices} that operate in the \gls{IOT}.
-Typically these edge devices are small microprocessors containing various sensors and actuators to interact with the physical world.
-They are often part of and coordinated by a bigger system called \gls{IOT} systems.
-The variety among the edge devices and the fact that they differ substantially from other devices makes it complex to program \gls{IOT} systems.
-
-%These ed
-%These edge devices differ very much from other devices we see around us.
-%Compared to servers, laptops, tablets, or mobile phones they boast tiny amounts of memory, are powered by a slow but energy efficient microprocessor, only support low-level programming languages, and are not so easily reprogrammed.
-%Moreover, these edge devices differ among eachother as well by using various microprocessor architectures, different communication protocols and using a variety of device-specific toolchains.
-%As a result, there are many points of failure and programming these systems is difficult and error-prone.
-%
-%\Gls{TOP} is a novel programming paradigm that offers a solution to this problem.
-%In a \gls{TOP} language, from a single declarative specification of the work that needs to be done, ready-for-work applications are generated for all layers of the system.
-%However, the hardware requirements for traditional \gls{TOP} frameworks make it not feasable to run these generated applications on resource-constrained edge devices.
-%
-%\Glspl{DSL} can overcome this limitation because domain-specific knowledge is built into the programming language, allowing for lower hardware requirements.
-%This thesis presents \gls{MTASK}, a \gls{TOP} \gls{DSL} for edge devices that can be fully integrated with \gls{ITASK}, a \gls{TOP} \gls{DSL} for distributed multi-user workflow systems.
-%With \gls{MTASK}, all layers of an \gls{IOT} system can be programmed from a single programming language in a single programming paradigm.
+Typically these edge devices are small microprocessors containing sensors and actuators to interact with the physical world.
+The variety within edge devices, and the fact that they differ substantially from other types of devices, makes it complex to program \gls{IOT} systems.\todo{make sentence logical}
+Hence, an \gls{IOT} programmer has to program each device and their interoperation using different programming paradigms, programming languages, and abstraction levels resulting in semantic friction.
+
+This thesis introduces research on the many aspects of orchestrating \gls{IOT} systems using \gls{TOP}.
+\Gls{TOP} is a novel programming paradigm for programming multi-tier workflow systems using a single declarative specification of the work that needs to be done.
+Using advanced compiler technologies, much of the internals and communication of multi-tier applications are automatically generated and the result of compilation is a ready-for-work application.
+Unfortunately, because the abstraction level is so high, the hardware requirements are too excessive to be suitable for the average edge device.
+
+This is where \glspl{DSL} come into play.
+\Glspl{DSL} are languages created with a specific domain in mind.
+Consequently, domain knowledge does not have to be expressed in the language itself but they can be built-in features, thus drastically reducing the hardware requirements even with high levels of abstraction.
+
+\section{Reading guide}
+On Wikipedia, a musical rhapsody is defined as follows \citep{wikipedia_contributors_rhapsody_2022}:
+\begin{quote}\emph{%
+ A \emph{rhapsody} in music is a one-movement work that is episodic yet integrated, free-flowing in structure, featuring a range of highly contrasted moods, colour, and tonality.}
+\end{quote}
+This thesis is structured as a pure functional rhapsody containing three episodes barded by the introduction and conclusion (\cref{chp:introduction,chp:conclusion}).
+\Cref{prt:dsl} is a paper-based---otherwise known as cumulative---episode providing insight in advanced \gls{DSL} embedding techniques.
+The chapters are readable independently.
+\Cref{prt:top} is a monograph showing \gls{MTASK}, a \gls{TOP} \gls{DSL} for the \gls{IOT}.
+Hence, the chapters are best read in order.
+\Cref{prt:tvt} is a journal article in which quantitative and qualitatively compares traditional tiered \gls{IOT} programming to tierless programming.
+The chapter is readable independently.
+
+The following sections provide background material on the \gls{IOT}, \glspl{DSL}, and \gls{TOP} after which a detailed overview of the contributions is presented.
+Text typeset as \texttt{teletype} represents source code.
+Standalone source code listings are used are marked with the programming language used.
+For the \gls{FP} language \gls{CLEAN}, a guide tailored to \gls{HASKELL} programmers is available as in \cref{chp:clean_for_haskell_programmers}.
\section{Internet of things}\label{sec:back_iot}
The \gls{IOT} is growing rapidly and it is changing the way people and machines interact with the world.
\emph{The \glsxtrlong{IOT}, or \glsxtrshort{IOT}, is the integration of people, processes and technology with connectable devices and sensors to enable remote monitoring, status, manipulation and evaluation of trends of such devices.}
\end{quote}
-CISCO states that the \gls{IOT} only started when there where as many connected devices as there were people on the globe, i.e.\ around 2008 \citep{evans_internet_2011}.
-Today, the \gls{IOT} is the term for a system of devices that sense the environment, act upon it and communicate with each other and the world.
+CISCO states that the \gls{IOT} started when there where as many connected devices as there were people on the globe, i.e.\ around 2008 \citep{evans_internet_2011}.
+Today, \gls{IOT} is the term for a system of devices that sense the environment, act upon it and communicate with each other and the world.
These connected devices are already in households all around us in the form of smart electricity meters, fridges, phones, watches, home automation, \etc.
When describing \gls{IOT} systems, a tiered---or layered---architecture is often used to compartmentalize the technology.
-The number of tiers heavily depends on the required complexity of the model but for the intents and purposes of the thesis, the four layer architecture shown in \cref{fig:iot-layers} is used.
+The number of tiers heavily depends on the required complexity of the model but for the intents and purposes of this thesis, the four layer architecture as shown in \cref{fig:iot-layers} is used.
\begin{figure}[ht]
\centering
\includestandalone{iot-layers}
- \caption{A four-layer \gls{IOT} architecture.}%
+ \caption{A four-tier \gls{IOT} architecture.}%
\label{fig:iot-layers}
\end{figure}
-Closest to the end-user is the presentation layer, it provides the interface between the user and the \gls{IOT} application.
-In home automation this may be a web interface or a app used on a phone or mounted tablet to interact with the edge devices and view the sensor data.
+To explain the tiers, an example \gls{IOT} application---home automation---is dissected accordingly.
+Closest to the end-user is the presentation layer, it provides the interface between the user and the \gls{IOT} system.
+In home automation this may be a web interface or an app used on a phone or mounted tablet to interact with the edge devices and view the sensor data.
-The application layer provides the \glspl{API}, interfaces and data storage.
-A cloud service or local server provides this layer in a typical home automation application.
+The application layer provides the \glspl{API}, data interfaces, and data storage of the \gls{IOT} system.
+A cloud server or local server provides this layer in a typical home automation application.
All layers are connected using the network layer.
In many applications this is implemented using conventional networking techniques such as WiFi or Ethernet.
-However, networks or layers on top of it tailored to the needs of \gls{IOT} applications have been increasingly popular such as \gls{BLE}, LoRa, ZigBee, LTE-M, or \gls{MQTT}.
+However, networks or layers on top of it---tailored to the needs of \gls{IOT} systems---have been increasingly popular such as \gls{BLE}, LoRa, ZigBee, LTE-M, or \gls{MQTT}.
The perception layer---also called edge layer---collects the data and interacts with the environment.
It consists of edge devices such as microprocessors equipped with various sensors and actuators.
-In home automation this layer consists of all the devices hosting the sensors and actuators such as in a smart lightbulb, an actuator to open a door or a temperature and humidity sensor.
+In home automation this layer consists of all the devices hosting the sensors and actuators such as a smart lightbulb, an actuator to open a door or a temperature and humidity sensor.
Across the layers, the devices are a large heterogeneous collection of different platforms, protocols, paradigms, and programming languages often resulting in impedance problems or semantic friction between layers when programming \citep{ireland_classification_2009}.
-Even more so, perception layer specifically often is a heterogeneous collections of microprocessors in itself as well, each having their own peculiarities, language of choice and hardware interfaces.
+Even more so, perception layer itself often is a heterogeneous collections of microprocessors in itself as well, each having their own peculiarities, language of choice, and hardware interfaces.
As the edge hardware needs to be cheap, small-scale, and energy efficient, the microprocessors used to power these devices do not have a lot of computational power, only a soup\c{c}on of memory, and little communication bandwidth.
-Typically the devices do not run a full fledged \gls{OS} but a compiled firmware.
-This firmware is often written in an imperative language that needs to be flashed to the program memory.
-Program memory typically is flash based and only lasts a couple of thousand writes before it wears out.
+Typically the devices do not run a full fledged \gls{OS} but a compiled firmware that written in an imperative language.
While devices are getting a bit faster, smaller, and cheaper, they keep these properties to an extent, greatly reducing the flexibility for dynamic systems where tasks are created on the fly, executed on demand, or require parallel execution.
+As program memory is mostly flash based and only lasts a couple of thousand writes before it wears out, it is not suitable for rapid reconfiguring and reprogramming.
+
These problems can be mitigated by dynamically sending code to be interpreted to the microprocessor.
With interpretation, a specialized interpreter is flashed in the program memory once that receives the program code to execute at runtime.
Interpretation always comes with an overhead, making it challenging to create them for small edge devices.
Programming languages can be divided up into two categories: \glspl{DSL}\footnote{Historically this has been called DSEL as well.} and \glspl{GPL} \citep{fowler_domain_2010}.
Where \glspl{GPL} are not made with a demarcated area in mind, \glspl{DSL} are tailor-made for a specific domain.
Writing idiomatic domain-specific code in an \gls{DSL} is easy but this may come at the cost of the \gls{DSL} being less expressive to an extent that it may not even be Turing complete.
-\Glspl{DSL} come in two main flavours: standalone and embedded\footnote{Also called external and internal respectively.} of which \glspl{EDSL} can again be classified into heterogeneous and homogeneous languages (see \cref{fig:hyponymy_of_dsls} for this hyponymy).
+\Glspl{DSL} come in two main flavours: standalone and embedded (\cref{sec:standalone_embedded})\footnote{Also called external and internal respectively.} of which \glspl{EDSL} can again be classified into heterogeneous and homogeneous languages (\cref{sec:hetero_homo}).
+This hyponymy is shown in \cref{fig:hyponymy_of_dsls}.
\begin{figure}[ht]
\centering
\label{fig:hyponymy_of_dsls}
\end{figure}
-\subsection{Standalone and embedded}
+\subsection{Standalone and embedded}\label{sec:standalone_embedded}
\glspl{DSL} where historically created as standalone languages, meaning all the machinery is developed solely for the language.
The advantage of this approach is that the language designer is free to define the syntax and type system of the language as they wish, not being restricted by any constraint.
Unfortunately it also means that they need to develop a compiler or interpreter for the language to be usable making standalone \glspl{DSL} costly to create.
Furthermore, errors shown to the programmer may be larded with host language errors, making it difficult for a non-expert of the host language to work with the \gls{DSL}.
Pure \gls{FP} languages are especially suitable for hosting embedded \glspl{DSL} because they have strong and versatile type systems, minimal but flexible syntax and offer referential transparency.
-\subsection{Heterogeneity and homogeneity}
+\subsection{Heterogeneity and homogeneity}\label{sec:hetero_homo}
\Citet{tratt_domain_2008} applied a notion from metaprogramming \citep{sheard_accomplishments_2001} to \glspl{EDSL} to define homogeneity and heterogeneity of \glspl{EDSL} as follows:
\begin{quote}
\section{\texorpdfstring{\Glsxtrlong{TOP}}{Task-oriented programming}}\label{sec:back_top}
\Gls{TOP} is a declarative programming paradigm designed to model interactive systems \citep{plasmeijer_task-oriented_2012}.
\Citet{steenvoorden_tophat_2022} defines two instruments for \gls{TOP}: \gls{TOP} languages and \gls{TOP} engines.
-A \gls{TOP} language is the formal language to specify workflows.
+A \gls{TOP} language is a language to specify workflows.\todo{improve sentence}
A \gls{TOP} engine executes such a specification as a ready-for-work application.
Instead of dividing problems into layers or tiers, as is done in \gls{IOT} architectures, it deals with separation of concerns in a novel way.
From the data types, utilising various \emph{type-parametrised} concepts, all other aspects are handled automatically (see \cref{fig:tosd}).
\label{fig:tosd}
\end{figure}
+\todo{describe relation with \gls{IOT} architecture}
\begin{description}
\item[\Glsxtrshort{UI} (presentation layer):]
The \gls{UI} of the system is automatically generated from the representation of the type.
The \gls{UOD} from the business layer is explicitly and separately modelled by the relations that exist in the functions of the host language.
\end{description}
-
\subsection{\texorpdfstring{\Gls{ITASK}}{ITask}}
The concept of \gls{TOP} originated from the \gls{ITASK} framework, a declarative workflow language and \gls{TOP} engine for defining multi-user distributed web applications implemented as an \gls{EDSL} in the lazy pure \gls{FP} language \gls{CLEAN} \citep{plasmeijer_itasks:_2007,plasmeijer_task-oriented_2012}.
From the structural properties of the data types, the entire user interface is automatically generated.
>>! \result->Hint "You Entered:" @>> viewInformation [] result[+\label{lst:task_comb}+]
\end{lstClean}
-\subsection{Other \texorpdfstring{\glsxtrshort{TOP}}{TOP} languages}
-While \gls{ITASK} conceived \gls{TOP}, it is not the only \gls{TOP} language and engine.
-Some \gls{TOP} languages and systems arose from Master's and Bachelor's thesis projects (e.g.\ \textmu{}Task \citep{piers_task-oriented_2016} and LTasks \citep{van_gemert_task_2022}) or were created to solve a practical problem (e.g.\ Toppyt \citep{lijnse_toppyt_2022} and hTask \citep{lubbers_htask_2022}).
-Furthermore, \gls{TOPHAT} is a fully formally specified \gls{TOP} language designed to capture the essence of \gls{TOP} formally \citep{steenvoorden_tophat_2019}.
-It is also possible to translate \gls{TOPHAT} code to \gls{ITASK} to piggyback on the \gls{TOP} engine it offers.
-
\subsection{\texorpdfstring{\Gls{MTASK}}{MTask}}
This thesis uses a novel \gls{TOP} language designed for defining workflows for \gls{IOT} edge devices \citep{koopman_task-based_2018}.
It is written in \gls{CLEAN} as a multi-view \gls{EDSL} and hence there are multiple interpretations of the language of which the byte code compiler is the most relevant for this thesis.
From the terms in the \gls{TOP} language, a very compact binary representation of the work that needs to be done is compiled.
This specification is then sent to a device that runs the \gls{MTASK} \gls{RTS}, a domain-specific \gls{TOP} engine implemented as a feather-light domain-specific \gls{OS}.
-\Gls{MTASK} is seemlessly integrated with \gls{ITASK}, it allows the programmer to define all layers of an \gls{IOT} system from a single declarative specification.
+\Gls{MTASK} is seamlessly integrated with \gls{ITASK}, it allows the programmer to define all layers of an \gls{IOT} system from a single declarative specification.
-\section{Reading guide and contributions}\label{sec:contributions}
-This novel view on programming \gls{IOT} systems is presented in the thesis as a purely functional rhapsody in three episodes.
-On Wikipedia, a rhapsody is defined as follows \citep{wikipedia_contributors_rhapsody_2022}:
-\begin{quote}
- \emph{A \emph{rhapsody} in music is a one-movement work that is episodic yet integrated, free-flowing in structure, featuring a range of highly contrasted moods, colour, and tonality.
- An air of spontaneous inspiration and a sense of improvisation make it freer in form than a set of variations.}
-\end{quote}
+\todo[inline]{Example application here, e.g.\ blink?}
+
+
+\subsection{Other \texorpdfstring{\glsxtrshort{TOP}}{TOP} languages}
+While \gls{ITASK} conceived \gls{TOP}, it is not the only \gls{TOP} language and engine.
+Some \gls{TOP} languages and systems arose from Master's and Bachelor's thesis projects (e.g.\ \textmu{}Task \citep{piers_task-oriented_2016} and LTasks \citep{van_gemert_task_2022}) or were created to solve a practical problem (e.g.\ Toppyt \citep{lijnse_toppyt_2022} and hTask \citep{lubbers_htask_2022}).
+Furthermore, \gls{TOPHAT} is a fully formally specified \gls{TOP} language designed to capture the essence of \gls{TOP} formally \citep{steenvoorden_tophat_2019}.
+It is also possible to translate \gls{TOPHAT} code to \gls{ITASK} to piggyback on the \gls{TOP} engine it offers \citep[\citesection{G.3}]{steenvoorden_tophat_2022}.
+
+\section{Contributions}\label{sec:contributions}
+This section provides a thorough overview of the relation to publications and the scientific contributions of the episodes and chapters.
\subsection{\nameref{prt:dsl}}
The \gls{MTASK} system is a heterogeneous \gls{EDSL} and during the development of it, several novel basal techniques for embedding \glspl{DSL} in \gls{FP} languages have been found.
repositories / phd-thesis.git / blobdiff