Luciano Gerber Alvaro A. A. Fernandes An Abstract Algebra for Knowledge Discovery in Databases. 83-98 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3255&spage=83 2004 conf/adbis/2004 ADBIS db/conf/adbis/adbis2004.html#GerberF04