Ontology Inference Layer OIL

Description of Ontology Inference Layer

The Ontology Inference Layer OIL is a proposal for a web-based representation and inference layer for ontologies, which combines the widely used modelling primitives from frame-based languages with the formal semantics and reasoning services provided by description logics. It is compatible with RDF Schema (RDFS), and includes a precise semantics for describing term meanings (and thus also for describing implied information).

OIL presents a layered approach to a standard ontology language. Each additional layer adds functionality and complexity to the previous layer. This is done such that agents (humans or machines) who can only process a lower layer can still partially understand ontologies that are expressed in any of the higher layers. The picture below sketches the relation between the OIL dialects and RDFS.

Core OIL coincides largely with RDF Schema (with the exception of the reification features of 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.
RDF Schema: http://www.w3.org/2000/01/rdf-schema#

Standard OIL is a language intended to capture the necessary mainstream modelling primitives that both provide adequate expressive power and are well understood thereby allowing the semantics to be precisely specified and complete inference to be viable.
Syntax: syntax/Standard-OIL/
RDF Schema: rdf-schema/2000/11/10-oil-standard#

Instance OIL includes a thorough individual integration. While the previous layer – Standard OIL – included modelling constructs that allow individual fillers to be specified in term definitions, Instance OIL includes a full-fledged database capability.
Syntax: syntax/Instance-OIL/
RDF Schema: rdf-schema/2000/11/10-oil-standard#
(note that Instance-OIL has the same schema as Standard-OIL; the instances are described directly in RDF)

Heavy OIL may include additional representational (and reasoning) capabilities.
Syntax: not yet defined
RDF Schema: not yet defined

An informal description of OIL-Instance and OIL-Standard (and thus of OIL Core) can be found in the white paper. 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. There is also an RDF Schema available for the preliminary version.

ontology inference layer oil