The BORO method is a simple, repeatable process for developing formal ontologies. The method takes an extensional approach to ontology development. The advantage of BORO over other methods is that its grounding in physical reality means that, if followed to the letter, the method will always produce the same ontology given the same inputs. This makes it particularly powerful for comparing multiple data-sources for semantic matches/mismatches and for re-engineering multiple legacy systems into a coherent whole (either as a new monolithic system, or as a method for designing federation of existing systems).