For machines, OIL uses RDF as its syntax. OIL exploits as much as possible the modelling primitives of RDF Schema. OIL has been designed to enable reasoning services that are sound and complete as well as efficient. Some constructions in DAML make similar reasoning services for DAML impossible. OIL one can state either sufficient conditions for a class, or conditions that are both sufficient and necessary.
OIL avoids such default values, because no clear formal semantics for default values exists.
It is unlikely that a single ontology language can fulfill all the needs of the large range of users and applications of the Semantic Web. We have therefore organised OIL as a series of ever increasing layers of sublanguages. Each additional layer will add functionality and complexity to the previous layer. A first and very important application of this principle is the relation between OIL and RDF Schema. 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.