OIL presents a layered approach to a standard ontology language.
Each additional layer adds functionality and complexity to the previous layer. This means that even simple RDF Schema agents are able to process the OIL ontologies, and pick up as much of their meaning as possible with their limited capabilities. The semantics are descibed in a separate document . Preliminary OIL is the previous definition of OIL, also known as OIL 1.0. This version is described in the technical report , and the syntax is descibed in DTD and a XML Schema .