Decision tree for merging classes from source ontologies into a unified single multi-species Uberon target ontology. The top part of the diagram shows the starting point, with a set of msAOs plus the original version of Uberon (Pre). Each class from the set of msAOs is checked for pre-existing equivalence axioms. If there are no equivalence axioms, a new Uberon class is generated; if there is an equivalence axiom, no new class is generated, but the ontology may be augmented with comments if there are differences in structure (e.g. not isomorphic).