No default is given for _chem_comp.mon_nstd_flag, and one of Helen's examples does not specify values. The natural default would seem to be sensitive to _chem_comp.id, i.e. "no" for standard amino acids and standard one-letter base codes and "yes" for everything else. Since this item is _not_ part of the key for chem_comp, it is proper to omit it, so some sort of statement as to the intended default would seem called for.