Graeme Richards Victor J. Rayward-Smith The discovery of association rules from tabular databases comprising nominal and ordinal attributes. 289-307 2005 9 Intell. Data Anal. 3 http://iospress.metapress.com/openurl.asp?genre=article&issn=1088-467X&volume=9&issue=3&spage=289 db/journals/ida/ida9.html#RichardsR05