Jue Wang Min Zhao Kai Zhao Suqing Han Multilevel data summarization from information systems: a "rule + exception" approach. 17-39 2003 16 AI Commun. 1 http://iospress.metapress.com/openurl.asp?genre=article&issn=0921-7126&volume=16&issue=1&spage=17 db/journals/aicom/aicom16.html#WangZZH03