P. Verheyden, J. Bo, and R. Meersman. Proc. of the 2nd Workshop on Semantic Web and Databases, VLDB Workshops
(SWDB 2004) (Toronto, Canada), page 109--126. Springer-Verlag, (2004)
G. Verheijen, and J. Bekkum. Proc. of the IFIP TC-8 Conference on Comparative Review of Information
System Methodologies (CRIS 82), North-Holland, (1982)
G. Varrò, A. Schürr, and D. Varró. Proc. IEEE Symp. Visual Languages (VL/HCC), Los Alamitos, University of Texas at Dallas, IEEE Press, (September 2005)