“Statistics and Ontology of Published Small Molecule Ring Systems” has recently been published. Diversity and properties of ring systems contained in small molecules are of high interest for applications such as drug discovery or material sciences. In the present work we extract, analyse and classify ring systems found in small molecule compounds of open access databases such as PubChem, ChEMBL, DrugCentral, IUPHAR or LOTUS. We also developed a classification taxonomy of frequently found ring systems using an OBO (Open Biomedical Ontologies) format ontology. Open access software was used to automate the classification of compounds into their respective ring system classes. As an example, the natural product compounds of the LOTUS database were classified and are available as an open access ontology data set.