G. Mineau, G. Stumme, and R. Wille. Conceptual Structures: Standards and Practices. Proc. ICCS '99, volume 1640 of LNAI, page 423-441. Heidelberg, Springer, (1999)
D. Jonassen, K. Beissner, and M. Yacci. LEA. Lawrence Erlbaum Associates, Hillsdale, NJ, (1993)David H. Jonassen, Katherine Beissner, Michael Yacci. Includes bibliographical
references and index. $5GBV.