## 2 Literature Overview
### Industry 4.0  
The Industry 4.0 concept refers to the fourth industrial revolution we are currently approaching. It is a combined result of effort made in all fields of technology. While the first industrial revolution mechanized production by using steam (the end of 18 th century to the beginning of 19 th century), the second one applied serial production by the means of electrification, oil, and natural gas (the end of 19 th century), and the third one automatized production via information technologies (the second half of 20 th century), the fourth industrial revolution starts along with 21 st century and third millennium AD with the key words of globalization, digitalization, and virtual reality [1]. A typical feature of Industry 4.0 is joining technologies from unrelated fields. It is hypothesized that the differences between biological, physical, and digital spheres will be gradually erased. The fourth industrial revolution emphasizes disciplines such as artificial intelligence (AI), robotics, internet of things (IoT), data analysis, material sciences, nanotechnology, biotechnology, etc., as well as their interconnection and transmitting knowledge from one discipline to another [2]. With the amount of attention Industry 4.0 is receiving lately, it is only natural that there are lots of studies trying to grasp its most important features and development. A paper by [PERSON] et al. (2021) summarizes trends and industrial prospects of the concept, laying ground rules and industry framework. They also identify Industry 4.0 as one of the world's most emerging areas for academicians and policymakers. In the study, the important aspects of the methodology are being viewed in the context of history, advantages, and challenges [3]. Among various maintenance strategies, the concept of a smart factory is gaining importance. [PERSON], [PERSON], [PERSON], and [PERSON] (2021) discuss this topic in their comprehensive investigation, capturing the current trends, critical aspects, and main difficulties of remote maintenance, self-maintenance, and autonomous maintenance [4]. A great topic of this century is the question of sustainability. However, as [PERSON], [PERSON], [PERSON], and [PERSON] (2021) suggest in their paper, the relation between sustainability and Industry 4.0 is still unclear, and the literature is fragmented on this point. Therefore, they peer-reviewed 117 journal articles to present a conceptualization and theoretical framework for the topic. Their focus is especially on the impact Industry 4.0 has, or presumably will have, on sustainability [5]. Sustainability is also one of the points which [PERSON] et al. (2021) analyzed in their bibliometric and systematic review, concerning also concepts and success determinants of Industry 4.0. The study worked with 745 articles dealing with the subject. It describes how the Industry 4.0 implications for value creating expand beyond the manufacturingindustry. The transformations to the new industrial revolution can, according to the study, address pressing issues of sustainable development goals, especially in the field of manufacturing/economic development [6]. [PERSON] et al. (2021) provide another contribution to the topic of sustainability. They use a systematic literature review of 127 articles to investigate the potential of Industry 4.0 to achieve manufacturing sustainability. The research uncovered that there is a fair amount of general discussion on the topic, but very few studies concern shop floor activities and different technologies in achieving manufacturing sustainability. There, they see opportunity for further discussions [7]. One of the biggest challenges of Industry 4.0 is dealing with the growing volumes of data and doing so close to real time. [PERSON], [PERSON], [PERSON], and [PERSON] present an approach (2021) to realize vertical data continuity with lean edge analytics.