An 'ontology' in the world of open data is a description of the relationship of data elements such as entities, attributes, fields, etc. within a specific context such as a data set, or involving other ontologies or vocabularies. Nanohistory's data model can be expressed in this manner using OWL RDF. The ontology itself is accessible at http://purl.org/nanohistory/ns if you're interested in using it. A visualization of the current ontology using WebOWL VOWL is below.