## 6 Conclusions and Future Work  
This study reports the planning and conducting phases of SMS. The SMS was based on the identification, analysis and classification of 90 selected published primary research papers, published from 1999 to 2019. Our goal was to identify and classify the CVs, and to investigate their impact in RE activities. In addition, we also extracted a set of data related to demographic aspects, such as the most active researchers, organizations and countries in the area. The SMS provides a broad view of the research area for the last 20 years. We selected 90 studies from 2348 papers retrieved by two complementary search strategies. The extracted data allow us to conclude that:  
* **RQ1:** Approximately 88% of the selected studies reported the use of ontologies and 12% focused on taxonomies. There is a lack of direct empirical evidence on the use of folksonomies or thesauri, although some studies reported their application, but were always embedded, as part of ontology or a thesaurus. * **RQ2:** The use of CVs has been studied in all RE activities, but not with the same interest. The applications have focused on the activities of elicitation (31%) and specification (32%), whereas the empirical support was reduced for the activities of analysis (20%), validation (13%) and change management (7%). * **RQ3:** The impacts with greater empirical support have been: guidance and understanding (39%), automation and support of tools (22%), and help to identify conflicts and defects (20%). Many of these impacts have overlapping effects, for example, by facilitating the understanding of the requirements, conflicts and possible defects are reduced, increasing the quality of the final specifications. Demographic data show that interest in CVs and their application in RE activities remain high in the research community. Several research groups, mainly in Europe, have been active since 2010, with an average, in the last 5 years, of eight articles published per year. Although most authors belong to academic organizations, there are also representatives from industry, government organizations and research institutes. A large part of the research is carried out in European organizations. The results highlight Pakistan as a very active country, with 12 mentions, however, its real participation is only two works (S54 and S71), with seven authors in the first study and five in the second (three researchers participated in both studies). On the other hand, the data show that the favorite publishing venues are Conferences and Workshops (almost 75% of the cases), which would suggest a greater participation of authors with industrial affiliations, however, their presence, based on the set of selected papers, is low (around 20%). We aim for the community to publish more collaborative works (academy-industry), to overcome the lack of industrial empirical evidence. As future work, we suggest that:  
* We believe it might be interesting to investigate the use of CVs in development environments based on open source models, where RE activities involve leveraging online comments and the wisdom of the crowd. * There is a need for more empirical research by conducting comprehensive review on how ontologies support the whole software engineering process. * In this SMS study, we did not find direct evidence on exploring the suitability and impact of folksonomies and thesauri on RE so it might be good to be investigated. * More collaborative empirical research needs to be conducted; more specifically, industrial-academic collaborations to evaluate the suitability of different CVs. * To conduct evaluation studies that can compare different RE processes supported by different types of controlled vocabularies used. Conceptualization, A.A. and J.L.B.J. ; methodology, A.A., J.L.B.J. and C.F. ; validation, A.A., J.L.B.J. and C.F. ; formal analysis, A.A., J.L.B.J. and C.F. ; data curation, A.A., and J.L.B.J. ; writing--original draft preparation, A.A., and J.L.B.J. ; writing--review and editing, A.A., J.L.B.J., A.A.K. and C.F.