PROCO (PROcess Chemistry Ontology) is a formal ontology that aims to standardly represent entities and relations among entities in the domain of process chemistry.This work is licensed under a Creative Commons Attribution 4.0 International License http://creativecommons.org/licenses/by/4.0/.THESE MATERIALS ARE PROVIDED AS IS AND WITHOUT ANY WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, INCLUDING, WITHOUT LIMITATION, THE WARRANTIES OF NON-INFRINGEMENT, TITLE, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.