Manouselis, Nikos, Charalampos Karagiannidis, and Demetrios G Sampson. “Layered Evaluation in Recommender Systems: A Retrospective Assessment”. Journal of e-Learning and Knowledge Society 10, no. 1 (January 25, 2014). Accessed October 17, 2021. https://www.je-lks.org/ojs/index.php/Je-LKS_EN/article/view/906.