Domain Ontologies in OSF
In the context of the open semantic framework, a domain ontology is the principal conceptual and descriptive structure for capturing the purpose of an OSF installation or the problem at hand. Domains are typically scoped to embrace the boundaries of this domain or problem space, and no more. They are generally comprised of domain concepts (or classes), coherently linked together in a logic structure that, when complete, forms a graph.
With respect to the population of ontologies that might be found on an OSF instance, the domain ontology is the most conceptual and descriptive. It defines the problem space for the users and consumers of the OSF installation. It plays no role in component or administrative aspects of the OSF portal.
Typically domain ontologies rely heavily on external ontologies, including those in related or overlapping domain areas. If possible, it is better to re-use existing concepts and ontologies than to reinvent existing concepts. (This is not a hard rule, however, since ultimately it is the purposes and scope of your domain problem that should determine these decisions, not an unquestioned choice for re-use.)
Breadth, depth, scope and extent of a domain ontology is highly variable, of course. It is also possible (indeed, advisable) to build your domain ontologies incrementally, learning and adding as you go. For more information on how to actually design and build a domain ontology, see the Lightweight, Domain Ontologies Development Methodology document.