Although the maximum rule length is set to 4, the length of all rules equals to 2. Small rule length here means compounds only share small number of fragments. The two rules that uniquely identified by IGAC is showed in indicates that if compounds contain fragment 50 and 60, they tend to be non-substrates. On the contrary, if compounds have fragment 77 and 117, they incline to be substrates by rule 19. The identified feature 117 matches the substructure mined by using SVM with ECFP_4 as feature . In addition, the preferred substructure of pgp substrate is reported to contain N, NH or O and the hydrogen bond acceptor or electron donor group is observed to be critical for P-gp substrate activity . Interestingly, rule 19 suggests if the compound has N and O-the potential hydrogen bond acceptor or electron donor group, then the compound is active.