M. Mavrikis, und S. Gutierrez-Santos. Computers & Education, 54 (3):
641 - 651(2010)Learning in Digital Worlds: Selected Contributions from the CAL 09 Conference.
E. Guy. Proceedings of ATIT 2004, The First International Workshop on Activity Theory Based Practical Methods for IT Design, Seite 33-48. Copenhagen, Denmark, Published as DAIMI report, University of Aarhus, (2004)