Table 2: Example of queries.

Digital libraryQuery

ScopusTITLE-ABS-KEY (“machine learning” OR “deep learning” OR “neuronal networks”) AND TITLE-ABS-KEY (“classifier” OR “classification” OR “classified” OR “classification system”) AND TITLE-ABS-KEY (“recommended” OR “recommender system” OR “collaborative filtering” OR “content-based filtering”)

IEEE Xplore(“Machine learning” OR “deep learning” OR “neuronal networks”) AND (“classifier” OR “classification” OR “classified” OR “classification system”) AND (“recommended” OR “recommender system” OR “collaborative filtering” OR “content-based filtering”)

ACMacmdlTitle: (“machine learning” “deep learning” “neuronal networks”) OR recordAbstract: (“machine learning” “deep learning” “neuronal networks”) AND (acmdlTitle: (“classifier” “classification” “classified” “classification system”) OR recordAbstract: (“classifier” “classification” “classified” “classification system”)) AND (acmdlTitle: (“recommended” “recommender system” “collaborative filtering” “content-based filtering”) OR recordAbstract: (“recommended” “recommender system” “collaborative filtering” “content-based filtering”))

Science direct(“Machine learning” OR “deep learning” OR “neuronal networks”) AND (“classifier” OR “classification” OR “classified” OR “classification system”) AND (“recommended” OR “recommender system” OR “collaborative filtering” OR “content-based filtering”)