Jaume Agustí-Cullell Jordi Puigsegur W. Marco Schorlemmer Query Answering by Means of Diagram Transformation. 15-28 http://link.springer.de/link/service/series/0558/bibs/1495/14950015.htm 1998 conf/fqas/1998 FQAS db/conf/fqas/fqas98.html#AgustiPS98