The GA was a SMILES fragment-based GA, with fragments of the molecules in the OPEP2 data set included in a library, represented as SMILES. This fragment library was divided into 3 classes: terminal groups (1 attachment point), fused core groups (4 or more fused rings), or spacer/unfused groups (3 or less fused rings). There were 69 terminal groups, 169 spacer/unfused groups, and 139 fused core groups.