Takashi Nakayama Semantic dictionary for substructure matching of chemical structures with general descriptors. 845-853 1994 34 Journal of Chemical Information and Computer Sciences 4 http://pubs.acs.org/cgi-bin/archive.cgi/jcisd8/1994/34/i04/f-pdf/f_ci00020a019.pdf db/journals/jcisd/jcisd34.html#Nakayama94