Wim Martens Frank Neven Thomas Schwentick Which XML Schemas Admit 1-Pass Preorder Typing? 68-82 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3363&spage=68 2005 conf/icdt/2005 ICDT db/conf/icdt/icdt2005.html#MartensNS05