Upper Ontology

An upper ontology is a high-level, domain-independent ontology that describes very general concepts — such as 'object', 'role', 'event', 'time', or, in a web-accessibility context, generic structural roles like 'menu', 'navigation', 'content region', or 'decoration'. It is designed to be extended by domain- or site-specific lower ontologies that map concrete entities (for example, a particular site's CSS classes) to the general concepts. Upper ontologies are a common architectural pattern in Semantic Web-based accessibility systems such as SADIe, because they let the core transcoding logic generalise across sites while each new site only requires a small, site-specific annotation step.