Pavel Zezula Federica Mandreoli Riccardo Martoglia Tree Signatures and Unordered XML Pattern Matching. 122-139 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2932&spage=122 2004 conf/sofsem/2004 SOFSEM db/conf/sofsem/sofsem2004.html#ZezulaMM04