Massimo Marchi Alessandra Mileo Alessandro Provetti Grid Service Selection with PPDL. 464-466 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3132&spage=464 2004 conf/iclp/2004 ICLP db/conf/iclp/iclp2004.html#MarchiMP04