has part has part has_part material entity material entity atom molecule Any constitutionally or isotopically distinct atom, molecule, ion, ion pair, radical, radical ion, complex, conformer etc., identifiable as a separately distinguishable entity. molecular entity A material entity that consists of two or more atoms that are all connected via covalent bonds such that any atom can be transitively connected with any other atom. This molecular entity is different than ChEBI's 'molecular entity'. We are assuming that every molecular entity has to be completely connected by chemical bonds. This excludes protein complexes, which are comprised of minimally two separate molecular entities. We will follow up with Chebi to ensure this is their understanding as well We would like to have cardinality restrictions on the logic, but there are some technical limitations.