Luciano Buratto Khalil Sima'an Backoff DOP: Parameter Estimation by Backoff. 35-42 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2807&spage=35 2003 conf/tsd/2003 TSD db/conf/tsd/tsd2003.html#BurattoS03