François Bry Stephanie Spranger Towards a Multi-calendar Temporal Type System for (Semantic) Web Query Languages. 102-117 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3208&spage=102 2004 conf/ppswr/2004 PPSWR db/conf/ppswr/ppswr2004.html#BryS04