Joachim Hereth Correia Tim B. Kaiser A Mathematical Model for TOSCANA-Systems: Conceptual Data Systems. 39-46 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2961&spage=39 2004 conf/icfca/2004 ICFCA db/conf/icfca/icfca2004.html#CorreiaK04a