# Digital Twin Lean Intralogistics: Research Implications
## 3 Methodology  
In this study, the following research methodology was chosen (Figure 4) considering works [17; 18]. Referring to Figure 4, a three-stage study was conducted to demonstrate research implications in the range of Digital Twin Lean Intralogistics. Figure 3: Industry 4.0 and Lean connection in the context of Digital Twin—based on [16]. Figure 2: Factory layout dynamics. **Stage I: Planning. ** At this stage, studies were planned that concerned the justification of research on the presented topic (step 1.1. ), the determination of research questions (step 1.2. ), and the specification of detailed selection criteria (step 1.3.). In order to justify undertaking research on the implication of the Digital Twin, Lean, and Intralogistics concepts, in accordance with the adopted methodology, a trend analysis was performed. The authors used Google Trends, which allows the analysis of words and phrases entered by users into the Google search engine. The results show the popularity of a search term within a given period and in a selected region. Data in Google Trends are normalized and presented in the range of 0 to 100. Normalization consists of finding the day on which Internet users in a given region and at a given time most often ask for the selected term in the Google search engine (compared to all searches in a given area and time). The obtained result is marked as 100. The following days are given numbers from 0 to 100 in proportion to the highest score. In the study related to the analysis of trends, the following preliminary research question was posed (hereinafter referred to as pRQ):  
* pRQ1: What is the extent of interest in terms such as: \"digital twin\", \"intralogistics\", \"lean intralogistics\", or \"digital twin lean intralogistics\"? * pRQ2: Has the digital revolution/Industry 4.0 influenced an increase in interest in digital twin? The research question pRQ1 results directly from the purpose of the research, while pRQ2 is a kind of derivative question indicating a relationship between 14.0 and Digital Twin technology, which was discussed in Section 2 of the article. The results of the study of trend analysis allowed the definition of the main research questions according to step 1.2. of the adopted research cycle methodology. It is therefore held that it is justified to conduct a literature analysis related to concepts such as Digital  
Figure 4: Research methodology. Twin, Lean intralogistics, and Digital Twin Lean Intralogistics. After justifying the need for literature research, research questions (RQ) were developed:  
* RQ1: Is scientific research related to digital twin being undertaken? * RQ2: Is research on lean intralogistics being undertaken? * RQ3: Is the application of digital twin in intralogistics based on lean philosophy being studied in the range of research on digital twin? In accordance with the adopted research methodology, in response to the indicated research questions (RQ1-RQ3), a detailed summary of the selection criteria used (hereinafter SC) was developed (step 1.3.). It is presented in Table 1.  
The research used several keywords (H1, H2, H3, H4) which combined issues such as digital twin, intralogistics, and lean, in accordance with the needs expressed in RQ. The keywords were presented in different notation variants. The literature research was planned to be carried out using logical operators AND, OR, making the appropriate combinations of keywords in the title, abstract, or keywords (Z1), or just in the title (Z2). There were no restrictions on the publication date, type of publication, or research area. However, due to the language of publication, searches were limited to English, which stemmed from the assumption that the relevant studies are mainly written in this language. The abstract and citation databases used in the research included Web of Science and Scopus. The selected databases are mainly used internationally in management studies and are also chosen by online libraries of major universities.