R. Azambuja Silveira, R. Lunardi Comarella, R. Lima Rocha Campos, J. Vian, and F. De La Prieta, “Learning Objects Recommendation System: Issues and Approaches for Retrieving, Indexing and Recomend Learning Objects”, ADCAIJ, vol. 4, no. 4, pp. 69–82, Dec. 2015.