Gösta Grahne Alex Thomo Query Answering and Containment for Regular Path Queries under Distortions. 98-115 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2942&spage=98 2004 conf/foiks/2004 FoIKS db/conf/foiks/foiks2004.html#GrahneT04