1Gerardo Ayala,Yoneo Yano.A collaborative learning environment based on intelligent agents[J].Expert Systems with Applications14(1998).129-137.
2Hassenplug,C.& Harnish,D.(1998).The nature and importance of interaction in Distance Education credit classes at technical institutes[J].Community College Journal of Research and Practice,22 (6),591-606.
3World declaration on higher education for the twenty-first century: vision and action [ DB/OL ].http://www.unesco.org/ education/educprog/wche/declaration_eng.htm, 2011-12-24.