# A Systematic Mapping Study on the Modernization of Legacy Systems to Microservice Architecture
## 3 Planning and Conducting the Mapping
### Planning
#### 3.1.1 Objectives and Research Questions  
The objective of this study is to provide a comprehensive understanding of the modernization of legacy systems based on MSA. To address the aforementioned objective, a set of six distinct research questions (RQs) were formulated. Each RQ is associated with a specific objective and a well-established set of performance metrics. These efforts are directed towards the organization and synthesis of the knowledge dispersed throughout the extant literature, with a particular focus on existing initiatives. Next, the questions of our mapping are presented:  
**RQ1:**: What initiatives have been proposed to support the modernization of legacy systems based on MSA? The purpose of this question is to gather evidence regarding the modernization initiatives proposed in the primary studies selected in our SMS. As a result, this question aims to present an overview concerning the classification of these initiatives (e.g., approaches, processes, or methodologies), so that new initiatives can be proposed. **RQ2:**: What application domains have benefited from having this initiative type? This question provides evidence of application domains that have benefited from such initiatives. The existence of such evidence can facilitate a deeper comprehension of the necessity for these applications and the features they require, which can vary according to each domain or subdomain. **RQ3:**: How were these initiatives evaluated? The objective of this question is to provide evidence of the validation procedures adopted in these initiatives, such as proof of concepts, case studies, and experiments. Thus, a comprehensive overview of the rigor and efficacy of these initiatives can be obtained. **RQ4:**: What evidence motivates the adoption of these solutions? This question summarizes evidence of the maturity of these initiatives. The information from this question can provide insights concerning the nature of these initiatives (e.g., academic, industrial, or mixed). Thus, an overview of the maturity of these initiatives among practitioners and researchers can be outlined. **RQ5:**: What are the quality attributes addressed by these initiatives? The goal of this question is to identify which quality attributes have been used in a microservice-based application during modernization. **RQ6:**: What activities are conducted by these initiatives? This question aims to provide evidence of activities used to modernize a legacy system based on MSA. To address the RQs that were formulated in this section, a search string was elaborated based on two key terms: modernization and microservice. These terms were linked to their synonyms by using the Boolean operator OR to form the main terms, which were combined by the Boolean operator AND. Specialists from different areas (i.e., systematic review, software engineering, and service-oriented systems) evaluated our search string in order to increase its reliability. Table 1 presents the search string utilized in our SMS. Regarding the publication databases, we followed particular criteria proposed by [PERSON] et al. (2017), [PERSON] et al. (2018), and [PERSON] et al. (2018), namely, (i) content update (i.e., how frequently publications are updated), (ii) the availability of full-text articles, (iii) the quality of results (i.e., the accuracy of the results returned by the search), and (iv) versatility to export the results (i.e., since a search typically results in a sizable volume of data, a mechanism to export the results is required).