Shiyong Lu Yezhou Sun Mustafa Atay Farshad Fotouhi A Sufficient and Necessary Condition for the Consistency of XML DTDs. 250-260 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2814&spage=250 2003 conf/er/2003w ER (Workshops) db/conf/er/erw2003.html#LuSAF03