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Advancements in Internet of Things (IoT), cloud and mobile computing have fostered the digital enrichment—or “digitization”—of physical products, which are gaining increasing relevance in practice. According to recent studies, global IoT spending will exceed USD 1 Trillion by 2021 and there will be over 25 billion IoT connections (KPMG, 2018). Porter and Heppelmann (2014) state that IT is “revolutionizing products [as …] IT is becoming an integral part of the product itself.” Senior business executives like GE’s former CEO Jeff Immelt (2015) are even proposing that “every industrial company in the coming age is also going to become a software and analytics company.” This reflects the increasing relevance of IT components’ (i.e., software, data analytics, cloud computing) integration into previously purely physical products. We call IT-enriched physical products, “digitized” products to differentiate them from purely intangible “digital” products, such as digital music, e-books, and software. Examples of digitized products include the Philips Hue smartphone-controllable lightbulb, Audi Connect internet-connected cars, or Rolls-Royce’s sensor-enabled pay per use jet engines.
Digitized products provide their producers with a wide range of opportunities to offer new functionality and product capabilities (e.g., autonomy) that traditional, physical products do not exhibit (Porter and Heppelmann, 2014). In addition, the digitization of products allows producers to continuously repurpose their offerings, by extending and/or changing the product functionality and, thus, enabling new value creation opportunities. Based on their re-programmability and connectivity, digitized products “remain essentially incomplete […] throughout their lifetime as users continue to add and delete […] and change […] functional capabilities” (Yoo, 2013). For instance, the Philips Hue connected lightbulb enables remote control of basic functions (e.g., switching on and off the light) as well as setting more advanced light scenes for day-to-day tasks (e.g., relax, read) via Amazon’s Alexa artificial intelligence assistant (Signify, 2019), offerings that were not intended use cases when Signify (previously known as Philips Lighting) created Hue in 2012. Thus, digitized products present limitless potentials for new functionality and unforeseen use cases, which provides them with a huge innovation capacity.
Despite the limitless potentials offered by digitized products, there has been a slow uptake of digitized products by businesses so far (Jernigan et al., 2016; Mocker et al., 2019). According to a 2016 MIT Sloan Management Review report (Jernigan et al., 2016) only 24% of the investigated firms were actively using IoT technologies – a key technology for digitized products. In a more recent research study Mocker et al. (2019) found that the median revenue share from digital offerings (i.e., solutions based on IT enriched products) in large companies only accounted for 5% of the total revenue of the investigated companies.
The slow uptake of digitized products might be explained by the challenges that firms face regarding the changing nature of digitized products. Pervasive digital technologies (such as IoT) change the nature of products by adding new functionality that was previously not part of the value proposition of the products/services (e.g., a pair of shoes embedded with sensors and connectivity allows joggers to have access to data regarding their run distance, speed, etc.) (Yoo et al., 2012). The addition of new functionality and use cases of digitized products makes it harder for producers to design and develop relevant products (Hui 2014). As described in the paper ‘Do Your Customers Actually Want a “Smart” Version of Your Product?’, “just because [firms] can make something with IoT technology doesn’t mean people will want it.” (Smith, 2017).
The shift in digitized products’ nature poses new challenges for producers along the entire product development process (Porter and Heppelmann, 2015; Yoo et al., 2012) and create a paradox in product digitization, described by Yoo et al. (2012) as the paradox of pace: while technology accelerates the rate of innovation, companies need to spend more time to digitize their products, extending time to market. The production of these digitized products also becomes more challenging, e.g., as companies need to deal with different clock-speeds of software and hardware development (Porter and Heppelman, 2015). The above-mentioned challenges suggest that producers need to better understand how they can generate value from their digitized products’ generative potentials.
The body of literature on digitized products has been growing in recent years. For instance, Herterich et al. (2016) investigate how digitized product affordances (i.e., potentials) enable industrial service innovation; Nicolescu et al. (2018) explore the emerging meanings of value associated with IoT; and Benbunan-Fich (2019) studies the impact of basic wearable sensors on the quality of the user experience. However, it remains unclear what it takes for firms to generate value with their digitized product potentials. This dissertation investigates this research gap.
Over the last decades, a tremendous change toward using information technology in almost every daily routine of our lives can be perceived in our society, entailing an incredible growth of data collected day-by-day on Web, IoT, and AI applications.
At the same time, magneto-mechanical HDDs are being replaced by semiconductor storage such as SSDs, equipped with modern Non-Volatile Memories, like Flash, which yield significantly faster access latencies and higher levels of parallelism. Likewise, the execution speed of processing units increased considerably as nowadays server architectures comprise up to multiple hundreds of independently working CPU cores along with a variety of specialized computing co-processors such as GPUs or FPGAs.
However, the burden of moving the continuously growing data to the best fitting processing unit is inherently linked to today’s computer architecture that is based on the data-to-code paradigm. In the light of Amdahl's Law, this leads to the conclusion that even with today's powerful processing units, the speedup of systems is limited since the fraction of parallel work is largely I/O-bound.
Therefore, throughout this cumulative dissertation, we investigate the paradigm shift toward code-to-data, formally known as Near-Data Processing (NDP), which relieves the contention on the I/O bus by offloading processing to intelligent computational storage devices, where the data is originally located.
Firstly, we identified Native Storage Management as the essential foundation for NDP due to its direct control of physical storage management within the database. Upon this, the interface is extended to propagate address mapping information and to invoke NDP functionality on the storage device. As the former can become very large, we introduce Physical Page Pointers as one novel NDP abstraction for self-contained immutable database objects.
Secondly, the on-device navigation and interpretation of data are elaborated. Therefore, we introduce cross-layer Parsers and Accessors as another NDP abstraction that can be executed on the heterogeneous processing capabilities of modern computational storage devices. Thereby, the compute placement and resource configuration per NDP request is identified as a major performance criteria. Our experimental evaluation shows an improvement in the execution durations of 1.4x to 2.7x compared to traditional systems. Moreover, we propose a framework for the automatic generation of Parsers and Accessors on FPGAs to ease their application in NDP.
Thirdly, we investigate the interplay of NDP and modern workload characteristics like HTAP. Therefore, we present different offloading models and focus on an intervention-free execution. By propagating the Shared State with the latest modifications of the database to the computational storage device, it is able to process data with transactional guarantees. Thus, we achieve to extend the design space of HTAP with NDP by providing a solution that optimizes for performance isolation, data freshness, and the reduction of data transfers. In contrast to traditional systems, we experience no significant drop in performance when an OLAP query is invoked but a steady and 30% faster throughput.
Lastly, in-situ result-set management and consumption as well as NDP pipelines are proposed to achieve flexibility in processing data on heterogeneous hardware. As those produce final and intermediary results, we continue investigating their management and identified that an on-device materialization comes at a low cost but enables novel consumption modes and reuse semantics. Thereby, we achieve significant performance improvements of up to 400x by reusing once materialized results multiple times.
The extracellular matrix (ECM) is the non-cellular part of tissues and represents the natural environment of the cells. Next to structural stability, it provides various physical, chemical, and mechanical cues that strongly regulate and influence cellular behavior and are required for tissue morphogenesis, differentiation, and homeostasis. Due to its promising characteristics, ECM is used in a wide range of tissue engineering and regenerative medicine approaches as a biomaterial for coatings and scaffolds. To date, there are two sources for ECM material. First, native ECM is generated by the removal of the residing cells of a tissue or organ (decellularized ECM; dECM). Secondly, cell-derived ECM (cdECM) can be generated by and isolated from in vitro cultured cells. Although both types of ECM were intensively used for tissue engineering and regenerative medicine approaches, studies directly characterizing and comparing them are rare. Hence, in the first part of this thesis, dECM from adipose tissue and cdECM from stem cells and adipogenic differentiated stem cells from adipose tissue (ASCs) were characterized towards their macromolecular composition, structural features, and biological purity. The dECM was found to exhibit higher levels of collagens and lower levels of sulfated glycosaminoglycans compared to cdECMs. Structural characteristics revealed an immature state of collagen fibers in cdECM samples. The obtained results revealed differences between the two ECMs that can relevantly impact cellular behavior and subsequently experimental outcome and should therefore be considered when choosing a biomaterial for a specific application. The establishment of a functional vascular system in tissue constructs to realize an adequate nutrient supply remains challenging. In the second part, the supporting effect of cdECM on the self‐assembled formation of prevascular‐like structures by microvascular endothelial cells (mvECs) was investigated. It could be observed that cdECM, especially adipogenic differentiated cdECM, enhanced the formation of prevascular-like structures. An increased concentration of proangiogenic factors was found in cdECM substrates. The demonstration of cdECMs capability to induce the spontaneous formation of prevascular‐like structures by mvECs highlights cdECM as a promising biomaterial for adipose tissue engineering. Depending on the purpose of the ECM material chemical modification might be necessary. In the third and last part, the chemical functionalization of cdECM with dienophiles (terminal alkenes, cyclopropene) by metabolic glycoengineering (MGE) was demonstrated. MGE allows the chemical functionalization of cdECM via the natural metabolism of the cells and without affecting the chemical integrity of the cdECM. The incorporated dienophile chemical groups can be specifically addressed via catalysts-free, cell-friendly inverse electron-demand Diels‐Alder reaction. Using this system, the successful modification of cdECM from ASCs with an active enzyme could be shown. The possibility to modify cdECM via a cell-friendly chemical reaction opens up a wide range of possibilities to improve cdECM depending on the purpose of the material. Altogether, this thesis highlighted the differences between adipose dECM and cdECM from ASCs and demonstrated cdECM as a promising alternative to native dECM for application in tissue engineering and regenerative medicine approaches.
IT governance: current state of and future perspectives on the concept of agility in IT governance
(2020)
Digital transformation has changed corporate reality and, with that, corporates’ IT environments and IT governance (ITG). As such, the perspective of ITG has shifted from the design of a relatively stable, closed and controllable system of a self-sufficient enterprise to a relatively fluid, open, agile and transformational system of networked co-adaptive entities. Related to the paradigm shift in ITG, this thesis aims to conceptualize a framework to integrate the concept of agility into the traditional ITG framework and to test the effects of such an extended ITG framework on corporate performance.
To do so, the thesis uses literature research and a mixed method design by blending both qualitative and quantitative research methods. Given the poorly understood situation of the agile mechanisms within the ITG framework, the building process of this thesis’ research model requires an adaptive and flexible approach which involves four different research phases. The initial a priori research model based on a comprehensive review of the extant literature is critically examined and refined at the end of each research phase, which later forms the basis of a subsequent research phase. As a result, the final research model provides guidance on how the conceptualized framework leads to better business/IT alignment as well as how business/IT alignment can mediate the effectiveness of such an extended ITG framework on corporate performance.
The first research phase explores the current state of literature with a focus on the ITG-corporate performance association. This analysis identifies five perspectives with respect to the relationship between ITG and corporate performance. The main variables lead to the perspectives of business/IT alignment, IT leadership, IT capability and process performance, resource relatedness and culture. Furthermore, the analysis presents core aspects explored within the identified perspectives that could act as potential mediators or moderators in the relationship between ITG and corporate performance.
The second research phase investigates the agile aspect of an effective ITG framework in the dynamic contemporary world through a qualitative study. Gleaned from 46 semi-structured interviews across various industries with governance experts, the study identifies 25 agile ITG mechanisms and 22 traditional ITG mechanisms that corporations use to master digital transformation projects. Moreover, the research offers two key patterns indicating to a call for ambidextrous ITG, with corporations alternating between stability and agility in their ITG mechanisms.
In research phase three, a scale development process is conducted in order to develop the agile items explored in research phase two. Through 56 qualitative interviews with professionals the evaluation uncovers 46 agile governance mechanisms. Moreover, these dimensions are rated by 29 experts to identify the most effective ones. This leads to the identification of six structure elements, eight processes, and eight relational mechanisms.
Finally, in research phase four a quantitative research approach through a survey of 400 respondents is established to test and predict the formulated relationships by using the partial least squares structural equation modelling (PLS-SEM) method. The results provide evidence for a strong causal relationship among an expanded ITG concept, business/IT alignment, and corporate performance. These findings reveal that the agile ITG mechanisms within an effective ITG framework seem critical in today’s digital age.
This research is unique in exploring the combination of traditional and agile ITG mechanisms. It contributes to the theoretical base by integrating and extending the literature on ITG, business/IT alignment, ambidexterity and agility, all of which have long been recognized as critical for achieving organizational goals. In summary, this work presents an original analysis of an effective ITG framework for digital transformation by including the agile aspect within the ITG construct. It highlights that is not enough to apply only traditional mechanisms to achieve effective business/IT alignment in today’s digital age; agile ITG mechanisms are also needed. Therefore, a novel ITG framework following an ambidextrous approach is provided consisting of traditional ITG mechanisms as well as newly developed agile ITG practices. This thesis also demonstrates that agile ITG mechanisms can be measured independently of traditional ITG mechanisms within one causal model. This is an important theoretical outcome that allows the current state of ITG to be assessed in two distinct dimensions, offering various pathways for further research on the different antecedents and effects of traditional and agile ITG mechanisms. Furthermore, this thesis makes practical contributions by highlighting the need to develop a basic governance framework powered by traditional ITG mechanisms and simultaneously increase agility in ITG mechanisms. The results imply that corporations might be even more successful if they include both traditional and agile mechanisms in their ITG framework. In this way, the uncovered agile ITG practices may provide a template for CIOs to derive their own mechanisms in following an ambidextrous approach that is suitable for their corporation.
Intralogistics operations in automotive OEMs increasingly confront problems of overcomplexity caused by a customer-centred production that requires customisation and, thus, high product variability, short-notice changes in orders and the handling of an overwhelming number of parts. To alleviate the pressure on intralogistics without sacrificing performance objectives, the speed and flexibility of logistical operations have to be increased. One approach to this is to utilise three-dimensional space through drone technology. This doctoral thesis aims at establishing a framework for implementing aerial drones in automotive OEM logistic operations.
As of yet, there is no research on implementing drones in automotive OEM logistic operations. To contribute to filling this gap, this thesis develops a framework for Drone Implementation in Automotive Logistics Operations (DIALOOP) that allows for a close interaction between the strategic and the operative level and can lead automotive companies through a decision and selection process regarding drone technology.
A preliminary version of the framework was developed on a theoretical basis and was then revised using qualitative-empirical data from semi-structured interviews with two groups of experts, i.e. drone experts and automotive experts. The drone expert interviews contributed a current overview of drone capabilities. The automotive experts interview were used to identify intralogistics operations in which drones can be implemented along with the performance measures that can be improved by drone usage.
Furthermore, all interviews explored developments and changes with a foreseeable influence on drone implementation.
The revised framework was then validated using participant validation interviews with automotive experts.
The finalised framework defines a step-by-step process leading from strategic decisions and considerations over the identification of logistics processes suitable for drone implementation and the relevant performance measures to the choice of appropriate drone types based on a drone classification specifically developed in this thesis for an automotive context.
Corporate entrepreneurship in the public sector: exploring the peculiarities of public enterprises
(2021)
Entrepreneurship is predominantly treated as a private-sector phenomenon and consequently its increasing importance in the public sector goes largely unremarked. That impedes the research field of entrepreneurship being capable of spanning multiple sectors. Accordingly, recent research calls for the study of corporate entrepreneurship (CE) as it manifests in the public sector where it can be labeled public entrepreneurship (PE). This dissertation considers government an essential entrepreneurial actor and is led by the central research question: What are the peculiarities of the public sector and how do they impact public enterprises’ entrepreneurial orientation (EO)?
Accordingly, this dissertation includes three studies focusing on public enterprises. Two of the studies set the scope of this thesis by investigating a specific type of organization in a specific context—German majority-government-owned energy suppliers. These enterprises operate in a liberalized market experiencing environmental uncertainties like competitiveness and business transformation.
The aims and results of the studies included in this dissertation can be summarized as follows: The systematic literature review illuminates the stimuli of and barriers to entrepreneurial activities in public enterprises and the potential outcomes of such activities discussed so far. The review reveals that research on EO has tended to focus on the private sector and consequently that barriers to and outcomes of entrepreneurial activities in the public sector remain under-researched. Building on these findings, the qualitative study focuses on the interrelated barriers affecting entrepreneurship in public enterprises and the outcomes of entrepreneurial activities being inhibited. The study adopts an explorative comparative causal mapping approach to address the above-mentioned research goal and the lack of clarity around how barriers identified in the public sphere are interrelated. Furthermore, the study bases its investigation on the different business segments of sales (competitive market) and the distribution grid (natural monopoly) to account for recent calls for fine-grained research on PE. Results were compared with prior findings in the public and private sector. That comparison indicates that the barriers revealed align with aspects discussed in prior research findings relating to both sectors. Examples include barriers associated with the external environment such as legal constraints and barriers originating from within the organization such as employee behavior linked to a value system that hampers entrepreneurial action. However, the most important finding is that a public enterprise’s supervisory board can hinder its progress, a finding running counter to those of previous private-sector research and one that underscores the widespread prejudice that the involvement of a public shareholder and its nominated board of directors has a negative effect on EO. The third study is quantitative (data collection via a questionnaire) and builds on both its predecessors to examine the little understood topic of board behavior and public enterprises’ social orientation as predictors of EO. The study’s results indicate that social orientation represses EO, whereas board strategy control (BSC) does not seem to predict EO. Regarding BSC, we find that the local government owners in our sample are less involved in BSC. The third study also examines board networking and finds its relationship with EO depends on the ownership structure of the public-sector organization. An important finding is that minority shareholders, such as majority privately-owned enterprises and hub firms, repress EO when engaging in board networking.
In summary, this doctoral thesis contributes to the under-researched topic of CE in the public sector. It investigates the peculiarities of this sector by focusing on the supervisory board and social oriented activities and their impact on the enterprise’s EO in the quantitative study. The thesis addresses institutional questions regarding ownership and the last study in particular contributes to expanding resource dependence theory, and invites a nuanced perspective: The original perspective suggests that interorganizational arrangements like interfirm network ties and equity holdings reduce external resource dependency and consequently improve firm performance. The findings within this thesis expose resource delivery to potential contrary effects to extend the understanding of interorganizational action with important implications for practice.
After more than three decades of electronic design automation, most layouts for analog integrated circuits are still handcrafted in a laborious manual fashion today. This book presents Self-organized Wiring and Arrangement of Responsive Modules (SWARM), a novel interdisciplinary methodology addressing the design problem with a decentralized multi-agent system. Its basic approach, similar to the roundup of a sheep herd, is to let autonomous layout modules interact with each other inside a successively tightened layout zone. Considering various principles of self-organization, remarkable overall solutions can result from the individual, local, selfish actions of the modules. Displaying this fascinating phenomenon of emergence, examples demonstrate SWARM’s suitability for floorplanning purposes and its application to practical place-and-route problems. From an academic point of view, SWARM combines the strengths of procedural generators with the assets of optimization algorithms, thus paving the way for a new automation paradigm called bottom-up meets top-down.
In today’s marketplace, the consumption of luxury goods is at a peak due to increasing global wealth and low interest rates, resulting in a vast supply of goods and services to which customer experiences are more relevant than ever before. One of the most recent developments in this field shows that consumers no longer simply purchase a product or service based on the fact sheet; they are also interested in the experience around the product. Successful brands must develop and maintain individual images to sustain their competitive advantage and build brand equity that is beneficial for customers and firms. Ideally, these will lead to satisfaction and loyalty between a brand, its products, and its customers. Existing research about brand experience and brand equity has mainly focused on functional aspects, which seem to differ for high-value luxury goods. Most studies have focused on industries like retail and fashion brands, sampling university students or visitors to shopping malls, and some have even mixed different types of industries together. This underpins the need for research within a single luxury industry with actual luxury customers who have a solid background with brand experiences.
The purpose of this study was to explore the brand experience spectrum within the automotive industry in Germany, particularly in the affordable luxury sport car sector. Identifying the factors and components that constitute, influence, or leverage/drive a brand experience from their perspective was a clear aim of the study. To achieve this, the study collected data from indepth interviews with German (n=60) respondents who had experience with affordable and luxury sport cars. The conceptual framework was based on two empirically tested models guiding this exploratory consumer research. The first model to build on was the consumerbased brand equity model, empirically tested by Çifci et al. (2016) and Nam et al. (2011). The second conceptual framework was Lemon and Verhoef’s (2016) customer journey model consisting of relevant touchpoints along the following three stages: pre-purchase, purchase, and post-purchase.
The findings of the research demonstrate that, although the six brand equity concepts – brand awareness, physical quality, staff behaviour, self-congruence, brand identification, and lifestyle – are broadly applicable in understanding customer experience in the affordable luxury car industry, the content of these dimensions differs from that suggested by the previous authors. The research established that cognitive and affective (or symbolic) components build the foundation of customer brand experience and supports Çifci et al.’s (2016) and Nam et al.’s (2011) study results. The study also identified brand trust as an important and highly relevant concept for customer brand experience in the luxury automotive car industry. Brand trust influences customer satisfaction and loyalty, therefore improving and complementing the existing model. Furthermore, the study confirmed Lemon and Verhoef’s (2016) process model of the customer journey and experience; however, it suggested two different customer journeys depending on the customers’ previous experience (first-time and experienced buyers). The differences between the two groups and the relevance of the journey touchpoints within the three purchase stages vary significantly in terms and are distinct. Identified key touchpoints for both groups are the contact to a dealer as well as information gathering online. Differences have been found in the length of purchase stages and across the customer journey. The study highlights the importance of trust, identification, and product quality for customer brand experience. Moreover, the findings of this study complement the brand equity model of Çifci et al. (2016) by adding the new concept of trust, which is highly relevant. The current knowledge is complemented by a new understanding and mapping of the customer journey for luxury sports cars in Germany. This study can assist practitioners and managers by providing a compass indicating which touchpoints are relevant to which customer group. Social value can be achieved by encouraging interactions between brand and consumer (e.g. central product launch events) and through brand-oriented interactions among consumers (e.g. dealer events, clubs, or communities). Customers are motivated to express their distinctiveness through product experience and brand identification (belonging/distinction) and to develop a loyal link to brands.
Ever since the 1980s, researchers in computer science and robotics have been working on making autonomous cars. Due to recent breakthroughs in research and devel- opment, such as the Bertha Benz Project [ZBS+14], the goal of fully autonomous vehicles seems closer than ever before. Yet a lot of questions remain unanswered. Especially now that the automotive industry moves towards autonomous systems in series production vehicles, the task of precise localization has to be solved with automotive grade sensors and keep memory and processing consumption at a mini- mum. This thesis investigates the Simultaneous Localization and Mapping (SLAM) prob- lem for autonomous driving scenarios on a parking lot using low cost automotive sensors. The main focus is herby devoted to the RAdio Detection And Ranging (RADAR) sensor, which has not been widely analyzed in an autonomous driving scenario so far, even though they are abundant in the automotive industry for ap- plications such as Adaptive Cruise Control (ACC). Due to the high noise floor, the radar sensor has widely been disregarded in the Intelligent Transportation Systems and Robotics communities with regards to SLAM applications. However in this thesis, it is shown that the RADAR sensor proves to be an affordable, robust and precise sensor, when modeling its physical properties correctly. In this regard, a GraphSLAM based framework is introduced, which extracts features from the RADAR sensor and generates an optimized map of the surroundings using the RADAR sensor alone. This framework is used to enable crowd based localization, which is not limited to the RADAR sensor alone. By integrating an automotive Light Detection and Ranging (LiDAR) and stereo camera sensor, a robust and precise localization system can be built that that is suitable for autonomous driving even in complex parking lot scenarios. It it is thereby shown that the RADAR sensor is strongly contributing to obtaining good results in a sensor fusion setup. These results were obtained on an extensive dataset on a parking lot, which has been recorded over the course of several months. It contains different weather conditions, different configurations of parked cars and a multitude of different trajectories to validate the approaches described in this thesis and to come to the conclusion that the RADAR sensor is a reliable sensor in series autonomous driving systems, both in a multi sensor framework and as a single component for localization.
Context: Fast moving markets and the age of digitization require that software can be quickly changed or extended with new features. The associated quality attribute is referred to as evolvability: the degree of effectiveness and efficiency with which a system can be adapted or extended. Evolvability is especially important for software with frequently changing requirements, e.g. internet-based systems. Several evolvability-related benefits were arguably gained with the rise of service-oriented computing (SOC) that established itself as one of the most important paradigms for distributed systems over the last decade. The implementation of enterprise-wide software landscapes in the style of service-oriented architecture (SOA) prioritizes loose coupling, encapsulation, interoperability, composition, and reuse. In recent years, microservices quickly gained in popularity as an agile, DevOps-focused, and decentralized service-oriented variant with fine-grained services. A key idea here is that small and loosely coupled services that are independently deployable should be easy to change and to replace. Moreover, one of the postulated microservices characteristics is evolutionary design.
Problem Statement: While these properties provide a favorable theoretical basis for evolvable systems, they offer no concrete and universally applicable solutions. As with each architectural style, the implementation of a concrete microservice-based system can be of arbitrary quality. Several studies also report that software professionals trust in the foundational maintainability of service orientation and microservices in particular. A blind belief in these qualities without appropriate evolvability assurance can lead to violations of important principles and therefore negatively impact software evolution. In addition to this, very little scientific research has covered the areas of maintenance, evolution, or technical debt of microservices.
Objectives: To address this, the aim of this research is to support developers of microservices with appropriate methods, techniques, and tools to evaluate or improve evolvability and to facilitate sustainable long-term development. In particular, we want to provide recommendations and tool support for metric-based as well as scenario-based evaluation. In the context of service-based evolvability, we furthermore want to analyze the effectiveness of patterns and collect relevant antipatterns. Methods: Using empirical methods, we analyzed the industry state of the practice and the academic state of the art, which helped us to identify existing techniques, challenges, and research gaps. Based on these findings, we then designed new evolvability assurance techniques and used additional empirical studies to demonstrate and evaluate their effectiveness. Applied empirical methods were for example surveys, interviews, (systematic) literature studies, or controlled experiments.
Contributions: In addition to our analyses of industry practice and scientific literature, we provide contributions in three different areas. With respect to metric-based evolvability evaluation, we identified a set of structural metrics specifically designed for service orientation and analyzed their value for microservices. Subsequently, we designed tool-supported approaches to automatically gather a subset of these metrics from machine-readable RESTful API descriptions and via a distributed tracing mechanism at runtime. In the area of scenario-based evaluation, we developed a tool-supported lightweight method to analyze the evolvability of a service-based system based on hypothetical evolution scenarios. We evaluated the method with a survey (N=40) as well as hands-on interviews (N=7) and improved it further based on the findings. Lastly with respect to patterns and antipatterns, we collected a large set of service-based patterns and analyzed their applicability for microservices. From this initial catalogue, we synthesized a set of candidate evolvability patterns via the proxy of architectural modifiability tactics. The impact of four of these patterns on evolvability was then empirically tested in a controlled experiment (N=69) and with a metric-based analysis. The results suggest that the additional structural complexity introduced by the patterns as well as developers' pattern knowledge have an influence on their effectiveness. As a last contribution, we created a holistic collection of service-based antipatterns for both SOA and microservices and published it in a collaborative repository.
Conclusion: Our contributions provide first foundations for a holistic view on the evolvability assurance of microservices and address several perspectives. Metric- and scenario-based evaluation as well as service-based antipatterns can be used to identify "hot spots" while service-based patterns can remediate them and provide means for systematic evolvability construction. All in all, researchers and practitioners in the field of microservices can use our artifacts to analyze and improve the evolvability of their systems as well as to gain a conceptual understanding of service-based evolvability assurance.