]. N. Capuano, M. Marsella, and S. Salerno, ABITS: An Agent Based Intelligent Tutoring System for Distance Learning, Proceeding of ITS 2000, 2000.

A. Cavallone, M. Gaeta, M. Marsella, and F. O. Hodgins, Distance Learning Models and Web Simulation Learning Object Metadata, Working Draft Document 2.5, Proceeding of International Conference on Web-based Modeling & Simulation, 1999.

J. Sowa, A. Cavallone, C. D-'apice, and M. , On conceptual structures, Artificial Intelligence, vol.34, issue.3, 1984.
DOI : 10.1016/0004-3702(88)90069-0

. Salerno, A web-based simulation environment for technical staff tutoring in computer network " proceeding of SCS Euromedia, 2000.

M. Hamalainen, A. B. Whinston, S. A. Vishik, and . Vv, Electronic Markets for Learning: Edication Brokerages on the Internet, IMS Metadata Specifications " , EDUCOM IMS project, 1996.