Definition: The chemical structure of a small molecule. Usage: Structure information is stored in the property structureData, in one of three formats: the CML format (see URL www.xml-cml.org), the SMILES format (see URL www.daylight.com/dayhtml/smiles/) or the InChI format (http://www.iupac.org/inchi/). The structureFormat property specifies which format is used. Examples: The following SMILES string describes the structure of glucose-6-phosphate: 'C(OP(=O)(O)O)[CH]1([CH](O)[CH](O)[CH](O)[CH](O)O1)'.
Source:http://www.biopax.org/release/biopax-level3.owl#ChemicalStructure