## 3 Materials and Methods
### Conducting the SLR on Lean DSC and Classification Framework  
After finalizing the review process plan, the results for conducting the SLR are described in this section and summarized in Figure 4. By combining the three keyword levels, 229 papers are found by searching in Scopus. Afterward, the results were limited to English journals and conference papers, obtaining 172 papers. Then, to address the main aim of the paper and obtain consistent results, the papers are removed based on the other  
Figure 3: Least debated digital technologies in SC. Figure 2: Most debated digital technologies in SC. mentioned exclusion criteria in Section 3.1.2 by reading the title, abstract, and keywords. A total of 58 papers are kept in the dataset after this step. Moreover, in the process of reading full papers, authors continuously checked the relevance of the papers to the main aim of the research by referring to the same group of criteria in Section 3.1.2. Therefore, after investigating all papers, 25 papers were kept. In the next step, to be sure about the completeness of the database, forward and backward snowballing were conducted [58]. In backward snowballing, 33 additional papers are found by investigating the reference list of each previously qualified paper. Then, forward snowballing is carried out on the citation list of the 25 originally qualified papers based on Scopus, which added 6 further papers to the database. Totally, 64 papers are investigated to construct a comprehensive content analysis. Microsoft Excel(r) is used to build a data extraction form including the following fields: 1. Paper Information (paper title, year of publication, name of authors, name of journal, related information about journals such as impact factor and journal quality--Q1, Q2, etc., number of citations to the paper), 2. Searching Information (keywords for finding the paper in Scopus, link to the manuscript webpage), 3. Preliminary Paper Analysis (paper keywords, subject area, applied digital technologies, applied methodology, the source for data collection, research gap, research questions, main findings, limitations, future directions), 4. Detailed Paper Analysis (summary of the main points, critical analysis, relevance to the goal of the present research). In order to minimize the bias in the whole process of selecting and analyzing the papers, all the authors had regular weekly meetings to discuss and solve any doubts for each paper from October 2020 to June 2021. Based on full paper reading and the data extraction form, a framework is proposed to classify the results, which is fruitful to pave the way for developing future research avenues in the next steps. The following subsections explain the structure of such a framework and the main motivations to consider each of its perspectives. Figure 4: Results of SLR search. Selecting the SC Perspectives for Analysis  
The framework adopted to analyze the retrieved papers on Lean DSC includes the following perspectives. It is worth noting that the assignment of papers to each perspective is not mutually exclusive. 1. [label=()]
2. Supply Chain Processes. The benefits brought by digital technologies to each individual SC process should be addressed [24] to illustrate their capability to enhance each single process and also identify the most related digital technologies. Moreover, Lean principles are mostly perceived by the existing literature as a tool for the improvement of the production process, and their adoption in the other SC processes is still scarce [19]. In this paper, the following list of SC processes was addressed based on the works by [59; 60] to make a comprehensive view of all SC activities: Procurement, Warehousing, Inventory Management, Manufacturing (Production), Transportation, Customer Relationship, Demand Forecasting, Marketing, and Pricing. It should be noted that by warehousing authors mean all the activities related to the organization of the warehousing process and products storage.