Enumerations for _Chem_comp_descriptor.Type (An open enumeration) 
INCHI 'InChi descriptor' 
INCHI_CHARGE 'InChi descriptor- charge layer' 
INCHI_FIXEDH 'InChi descriptor- fixed hydrogren layer' 
INCHI_ISOTOPE 'InChi descriptor- isotopic layer' 
INCHI_MAIN 'InChi descriptor- main layer' 
INCHI_MAIN_CONNECT 'InChi descriptor- main layer - atom connection sub-layer' 
INCHI_MAIN_FORMULA 'InChi descriptor- main layer - chemical formula sub-layer' 
INCHI_MAIN_HATOM 'InChi descriptor- main layer - hydrogen atom sub-layer' 
INCHI_RECONNECT 'InChi descriptor- reconnected layer' 
INCHI_STEREO 'InChi descriptor- stereochemical layer' 
SMILES 'SMILES descriptor' 
SMILES_CANNONICAL deprecated 
SMILES_CANONICAL 'Canonical SMILES descriptor'