Gregor Engels Reiko Heckel Alexey Cherchago Flexible Interconnection of Graph Transformation Modules. 38-63 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3393&spage=38 2005 conf/birthday/2005ehrig Formal Methods in Software and Systems Modeling db/conf/birthday/ehrig2005.html#EngelsHC05