Damien K. Fisher Franky Lam Raymond K. Wong Algebraic Transformation and Optimization for XQuery. 201-210 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3007&spage=201 2004 conf/apweb/2004 APWeb db/conf/apweb/apweb2004.html#FisherLW04