Tony Clark Andy Evans Paul Sammut James S. Willans Transformation Language Design: A Metamodelling Foundation. 13-21 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3256&spage=13 2004 conf/gg/2004 ICGT db/conf/gg/icgt2004.html#ClarkESW04