Explicit. Includes all explicit evaluations carried out by experts and users.
Implicit. Taken from the implicit usage data for the materials, such as number of visits, number of times it is bookmarked by users, number of times it is downloaded, etc.
Characteristical. Descriptive information on the characteristics of the materials obtained from the metadata.
J. Sanz-Rodríguez is with the University Carlos III of Madrid, Av. Universidad 30, 28911 Leganés, Madrid, Spain.
J.M. Dodero is with the University of Cádiz, C/Chile, s/n, 1003 Cádiz, Spain. E-mail: email@example.com.
S. Sánchez-Alonso is with the University of Alcalá de Henares, Ctra. Barcelona km. 33600, 28871 Alcalá de Henares, Madrid, Spain.
Manuscript received 5 Feb. 2010; revised 21 Apr. 2010; accepted 2 Aug. 2010; published online 17 Aug. 2010.
For information on obtaining reprints of this article, please send e-mail to: firstname.lastname@example.org, and reference IEEECS Log Number TLT-2010-02-0011.
Digital Object Identifier no. 10.1109/TLT.2010.23.