Foto N. Afrati Vassia Pavlaki Rewriting queries using views with negation. 229-237 2006 19 AI Commun. 3 http://iospress.metapress.com/openurl.asp?genre=article&issn=0921-7126&volume=19&issue=3&spage=229 db/journals/aicom/aicom19.html#AfratiP06