## 1 Introduction  
The Fourth Industrial Revolution is profoundly changing the structures and processes within companies. Industry 4.0 is a one-time event that brings opportunities and challenges for large-sized enterprises, as well as for SMEs [1, 2]. Big companies have deployed investment plans, roadmaps, and worldwide investigation groups to support the transition toward Industry 4.0. The close relationship between a large-sized enterprise and an SME requires both advancing and progressing at the same speed. Therefore, SMEs must adapt to Industry 4.0 developments proposed by large companies. To cope with this transformation and be able to adopt Industry 4.0 innovations, SMEs must demonstrate flexibility and adaptability. However, many SMEs still find it difficult to know which Industry 4.0 technologies to invest in [3, 4, 5].  
Research and European initiatives in recent years proved that SMEs must be considered independently from large-sized enterprises regarding Industry 4.0 implementation, because they are less capable of handling the financial, technological, and staffing challenges than large companies [6, 7, 8, 9, 10]. The Fourth Industrial Revolution could end up being an obstacle to support firm competitiveness and productivity if the SMEs' peculiarities are not properly identified and supported. To gain a better insight into the characteristics of SMEs adopting Industry 4.0 technologies, the authors performed a systematic literature review to understand the challenges and problems that SMEs are facing during the Industry 4.0 transformation. Some authors refer to financial resources and technology awareness as the primary challenges that the SMEs are facing.  
Other research points out high costs, a lack of information, complexity, and the abundance of technologies as the key challenges and problems. However, all of them agree on one challenge: a lack of knowledge [1; 2; 3; 4; 5; 11; 12]. SMEs have problems accessing Industry 4.0 knowledge due to the lack of knowledge management and transfer.  
Knowledge management (KM) is a field of study that has existed for more than four decades [13]. It can be defined as the process of creating, sharing, using, and managing the knowledge and information of an organization [14; 15]. KM has four primary activity areas or knowledge flows, as shown in Figure 1: knowledge creation, retention, transfer, and utilization [16; 17].  
This research focuses on Industry 4.0 knowledge transfer (KT) within SMEs, as this was the primary challenge identified during the literature review. KT, sometimes also known as knowledge sharing (KS), refers to sharing knowledge from one individual or group of individuals (e.g., an SME) to another individual or group of individuals. KT pursues to create, organize, and distribute knowledge between different users and seeks to ensure its availability to future users [15; 16; 17; 18]. KT is a complex field because of the plurality of sources, including individuals, organizations, the internet, and books. Some aspects hindering successful KT are communication issues, a lack of networking and difficulty accessing the knowledge [19; 20]. Therefore, the ability to transfer knowledge effectively in the networks of SMEs is of paramount importance for supporting the transition to Industry 4.0. Several studies suggest the development of online platforms to optimize KT [21; 22]. These kinds of platforms promote a knowledge-sharing culture through discussion forums and other transfer tools so that SMEs contribute to the overall success.  
The authors consider two aspects to be crucial for the success of SMEs: the improvement of the access to Industry 4.0 knowledge and Industry 4.0 KT. For that reason, this research aims to fulfil the following research objectives:  
1. Analyze the existing KT initiatives and platforms supporting the Industry 4.0 transition within SMEs;
2. Propose a new collaborative online platform to improve Industry 4.0 KT between SMEs.  
Figure 1: Knowledge management and the four knowledge flows.