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Last modified: October 31, 2002
Ontology Interchange Language (OIL)

[September 16, 2000] OIL proposes a "a joint standard for integrating ontologies with exisiting and arising web standards. OIL is 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. Furthermore, OIL is the first ontology representation language that is properly grounded in W3C standards such as RDF/RDF-Schema and XML/XML-Schema." The development of OIL is governed by a Steering Commitee and an Advisory Board; the project is sponsored by the European Community via the IST projects Ibrow and On-to-knowledge.

As described in the white paper: "OIL unifies three important aspects: Formal semantics and efficient reasoning support as provided by Description Logics, epistemological rich modeling primitives as provided by Frame languages, and a standard proposal for syntactical exchange notations as provided by the Web community. (1) Description Logics describe knowledge in terms of concepts and role restrictions that are used to automatically derive classification taxonomies. They provide theories and systems for expressing structured knowledge, for accessing it and reason-ing with it in a principled way. (2) Frame-based systems provide as central modeling primitive classes (i.e., frames) with certain properties called attributes. These attributes do not have a global scope but are only applicable to the classes they are defined for. A frame provides a certain context for modeling one aspect of a domain. (3) Web standards: XML and RDF. Given the current dominance and importance of the WWW, a syntax of an ontology language must be formulated using existing web standards for information representation. The XML schema syntax of OIL was mainly defined as an extension of XOL. OIL is also defined on top of the Resource Description Framework RDF and RDF schema."

[August 16, 2001]   W3C Web Ontology Working Group Formed to Extend the 'Semantic Reach' of XML/RDF Metadata Efforts.    A posting from Dan Connolly to the W3C 'www-rdf-logic' mailing list announces the formation of a new Web Ontology Working Group within W3C. The Web Ontology (WebOnt) Working Group has been chartered to design a web ontology language "that builds on current web languges that allow the specification of classes and subclasses, properties and subproperties (such as RDFS), but which extends these constructs to allow more complex relationships between entities including: means to limit the properties of classes with respect to number and type, means to infer that items with various properties are members of a particular class, a well-defined model of property inheritance, and similar semantic extensions to the base languages. The web ontology language must support the development and linking of ontologies together, in a web-like manner. The products of this working group must be supported by a formal semantics allowing language designers, tool builders, and other 'experts' to be able to precisely understand the meaning and 'legal' inferences for expressions in the language. The language will use the XML syntax and datatypes whereever possible, and will be designed for maximum compatibility with XML and RDF language conventions." [Full context]


  • OIL Home Page

  • OIL XML DTD page, [cache]

  • XML-Schema for OIL, [cache]

  • OIL RDF schema page, [cache]

  • Technical description

  • A Denotational Semantics for OIL-Lite and Standard Oil By I. Horrocks, Department of Computer Science University of Manchester, UK.

  • Overview

  • [October 31, 2002] "DAML+OIL: An Ontology Language for the Semantic Web." By Deborah L. McGuinness (Stanford University), Richard Fikes (Stanford University), James Hendler (University of Maryland), and Lynn Andrea Stein (Franklin W. Olin College of Engineering). In IEEE Intelligent Systems [ISSN: 1094-7167] Volume 17, Number 5 (September/October 2002), pages 72-80. "By all measures, the Web is enormous and growing at a staggering rate. This growth has made it both increasingly difficult and increasingly important for humans and programs to quickly and accurately access Web information and services. A semantic Web-in which meanings of terms are captured and exploited-can provide the foundation for convenient Web content access. The DARPA Agent Markup Language (DAML) program aims to provide a language and toolset that enables the Web to transform from a platform that focuses on presenting information to a platform that focuses on understanding and reasoning with information. In this article, we describe the DAML language; its goal is to capture term meanings, and thereby providing a Web ontology language. In addition to a brief history of the language's evolution, we introduce the ontology language DAML+OIL by way of examples and include an axiomatization of the language... We're developing DAML+OIL in stages. Our initial aim was to capture term descriptions, as we've described here. The DAML program is now working on a query language and the integration of a rule-encoding option. The next major language enhancement, DAML-Logic (DAMLL) will address encoding inference and general implications. The DAML Services group also built a Web service ontology, DAML-S, which uses DAML+OIL to provide a foundation for Web agents. DAML+OIL was submitted as the starting point for the W3C Semantic Web Activity's OWL. The W3C's Web Ontology Working Group has produced a set of requirements for OWL, as motivated by a collection of use cases. DAML+OIL meets the current requirements draft reasonably well, and the initial OWL language description is quite similar to DAML+OIL. We believe that DAML+OIL is a useful starting point for describing Web content, building on decades of research in framebased systems, description logics, and Web languages. Given this foundation, and the research benefits into languages, complexity, and usability it provides, DAML+OIL could serve as a sound foundation for the next evolution of Web access. Researchers have already accepted DAML+OIL as a starting point for Web semantics representation and used it for applications ranging from military intelligence to medical and genetic database integration. Among the current development efforts are those focusing on using DAML+OIL for managing large Web sites and document and image collections, integrating disparate databases, and providing Web services' interoperability..."

  • [December 04, 2000] Freeware OilEd Ontology Editor. Ian Horrocks (University of Manchester) posted an announcement for an 'OilEd Ontology Editor' supporting the Ontology Interchange Language (OIL). "OilEd is a simple ontology editor developed by Sean Bechhofer at the University of Manchester. OilEd allows the user to: (1) build ontologies; (2) use the FaCT reasoner to check the consistency of ontologies and add implicit subClassOf relations; (3) export ontologies in a number of formats including both OIL-RDF and DAML-RDF. For further details and information about OIL, consult the OIL Home Page. The intention behind OilEd is to provide a simple, freeware editor that demonstrates the use of, and stimulates interest in, OIL. OilEd is not intended as a full ontology development environment - it will not actively support the development of large-scale ontologies, the migration and integration of ontologies, versioning, argumentation and many other activities that are involved in ontology construction. Rather, it is the 'NotePad' of ontology editors, offering just enough functionality to allow users to build ontologies and to demonstrate how the FaCT reasoner can be used to check and enrich ontologies. OilEd is available as freeware, but we ask that you provide us with some details before downloading. This will allow us to keep track of who is using it and why. OilEd will not be fully supported or maintained although we will try and fix major problems or bugs. You can download the installer for OilEd. The development of OilEd was supported by the University of Manchester, the Free University of Amsterdam and Interprice GmbH. OilEd uses Robert Kosara's Bonfire parser generator and the JGL collection libraries from Objectspace."

  • White paper This document provides an informal description of the modeling primitives of the OIL dialects "OIL-Lite" and "Standard OIL". It only gives a compact and informal description of these languages, plus a simple illustrative example. For more discussion and motivation, see the project papers. OIL's machine readable syntax is defined as an XML DTD, an XML Schema definition, and an RDF Schema definition. To improve human readability OIL, also has a more compact pseudo syntax where keywords are indicated by bold faced text, and grouping of sub-content is indicated by indentation. The formal definition of this human-readable syntax can be found at In this document, we give an informal description of this human-readable syntax, since it is the easiest way to get acquainted with the modelling primitives of the language. We refer to the above URLs for the formal definitions." [cache]

  • [March 28, 2001]   Updated DAML+OIL Language Specification Supports W3C XML Schema Data Types.    A posting from Mike Dean (Chair, Joint US/EU ad hoc Agent Markup Language Committee) announces the release of a new DAML+OIL 'semantic [ontology] markup language' specification which includes support for XML Schema Part 2: Datatypes and provides enhanced documentation. The DARPA Agent Markup Language (DAML) "is being developed as an extension to XML and the Resource Description Framework (RDF). The latest release of the language (DAML+OIL) provides a rich set of constructs with which to create ontologies and to markup information so that it is machine readable and understandable." The reference description document characterizes DAML+OIL as "a semantic markup language for Web resources. It builds on earlier W3C standards such as RDF and RDF Schema, and extends these languages with richer modelling primitives. DAML+OIL provides modelling primitives commonly found in frame-based languages. The language has a clean and well defined semantics. A DAML+OIL knowledge base is a collection of RDF triples. DAML+OIL prescribes a specific meaning for triples that use the DAML+OIL vocabulary. The model-theoretic semantics specifies exactly which triples are assigned a specific meaning, and what this meaning is. DAML+OIL only provides a semantic interpretation for those parts of an RDF graph that instantiate the schema defined in daml+oil.daml. Any additional RDF statements, resulting in additional RDF triples are perfectly allowed, but DAML+OIL is silent on the semantic consequences (or lack thereof) of such additional triples." The new '(March 2001)' version of DAML+OIL support documents include the revised language specification, a revised example ontology, the W3C "XSD" datatype definitions set used in the above example, an annotated version of the example ontology, systematic reference description of all the language elements, an explanation of the changes from DAML+OIL (December 2000), revised Model-Theoretic Semantics, and a revised Axiomatic Semantics. [Full context]

  • "OIL ontology inference and interchange." ECAI 2000 presentation by Frank van Harmelen. [cache]

  • DAML-ONT and OIL. "This page attempts to provide information concerning OIL- The Ontology Inference Layer - from the perspective of a reader interested in DAML and its evolution. There is an active discussion going on the www-rdf-logic mailing list concerning the evolution of the DAML ontology language and its relations to OIL, thus it may be useful to read some background information." See "DARPA Agent Mark Up Language (DAML)."

  • "OIL in a nutshell." By D. Fensel, I. Horrocks, F. Van Harmelen, S. Decker, M. Erdmann, and M. Klein. 12 pages. In Knowledge Acquisition, Modeling, and Management. Proceedings of the European Knowledge Acquisition Conference (EKAW-2000). Lecture Notes in Artificial Intelligence, LNAI, Springer-Verlag, October 2000. "Currently computers are changing from single isolated devices to entry points in a world wide network of information exchange and business transactions. Therefore, support in data, information, and knowledge exchange becomes the key issue in current computer technology. Ontologies provide a shared and common understanding of a domain that can be communicated across people and application systems. Ontologies will play a major role in supporting information exchange processes in various areas. A prerequisite for such a role is the development of a joint standard for specifying and exchanging ontologies. The purpose of the paper is precisely concerned with this necessity. We will present the Ontology Interchange Language OIL which is a proposal for such a standard. It is based on existing proposals such as OKBC, XOL and RDF and enrich them with necessary features for expressing ontologies. The paper sketches some of the main ideas of OIL." [cache]

  • "Adding formal semantics to the Web: building on top of RDF Schema." By Jeen Broekstra, Michel Klein and Dieter Fensel. "RDF Schema provides means to define vocabulary, structure and constraints for expressing metadata about Web resources. However, formal semantics for the primitives defined in RDF Schema are not provided, and the expressivity of these primitives is not enough for full-fledged ontological modeling and reasoning. To perform these tasks, an additional layer on top of RDF Schema is needed. In this paper, we will show how RDF Schema can be extended in such a way that a full knowledge representation language can be expressed in it, thus enriching it with the required additional expressivity and the semantics of this language. We do this by describing the ontology language OIL as an extension of RDF Schema. First, we give a short introduction to both RDF Schema and OIL. We then proceed to define a Schema to express OIL ontologies in RDF, where the aim is to use existing RDF terminology where possible, and extending RDF(S) where necessary. The result is an RDF Schema definition of OIL primitives, which allows one to express any OIL ontology in RDF syntax, thus enabling the added benefits of OIL, such as reasoning support and formal semantics, to be used on the Web. We conclude that our method of extending is equally applicable to other knowledge representation formalisms." Note: typo in Figure 4: the second "class-def plant" should be "class-def branch". [cache]

  • "The Relation between Ontologies and Schema-Languages: Translating OIL-Specifications to XML-Schema." By M.C.A. Klein et al. In Proceedings of the Workshop on Applications of Ontologies and Problem-solving Methods, 14th European Conference on Artificial Intelligence ECAI-00, Berlin, Germany August 20-25, 2000. "This paper compares OIL with XML schemas. Ontologies will play a major role in supporting information exchange processes in various areas. However, in order to develop their full power, the representation languages for ontologies must be comparative with existing data exchange standards in the World Wide Web. Therefore, we compare the two main standardization efforts in these areas. We will compare OIL the arising standard for exchanging ontologies with XML schemas which is the arising standard for describing structure and semantics of Web documents." [cache]

  • "The Ontology Inference Layer OIL." By I. Horrocks, D. Fensel, J. Broekstra, S. Decker, M. Erdmann, C. Goble, F. van Harmelen, M. Klein, S. Staab, R. Studer, and E. Motta. "Currently computers are changing from single isolated devices to entry points in a world wide network of information exchange and business transactions. Therefore, support in data, information, and knowledge exchange becomes the key issue in current computer technology. Ontologies provide a shared and common understanding of a domain that can be communicated across people and application systems. Ontologies will play a major role in supporting information exchange processes in various areas. A prerequisite for such a role is the development of a joint standard for specifying and exchanging ontologies. The purpose of the paper is precisely concerned with this necessity. We will present the Ontology Interchange Language OIL which is a proposal for such a standard. It is based on existing proposals such as OKBC, XOL and RDF and enrich them with necessary features for expressing rich ontologies. The paper presents motivation, underlying rationale, modeling primitives, syntax, semantics, and tool environment of OIL. With OIL, we want to make a proposal opening the discussing process that may lead to a useful and well defined consensus of a large community making use of such an approach. . . XML can be used as a serial syntax for OIL. Such a syntax is very useful because it puts OIL in the mainstream of tools that are currently being developed for supporting XML-based documents. Validation and rendering techniques developed for XML can directly be used for ontologies specified in OIL. Therefore, the appendix of this paper provides the definition of a DTD that defines constraints on valid documents in OIL. . . The relationship between OIL and RDF/RDFS is much closer than that between OIL and XML Schemas. This is not surprising, since XML-schema was meant to generalize the way of defining the structure of valid XML-documents and RDF/RDFS was meant to capture meaning in the manner of semantic nets. In the same way as RDF-Schema is used to define itself it can also be used to define other ontology languages. We have therefore defined a syntax for OIL by giving an RDF-schema for the core of OIL, and proposing related RDF-schemas that could complement this core by covering further aspects. To ensure maximal compatibility with existing RDF/RDFS-applications and vocabularies, the integration of OIL with the resources defined in RDF-schema has been a main focus in designing the RDF-model for OIL. [Conclusion:] In this paper, we have proposed both a syntax and a semantics of an ontology inference layer for the WWW based on XML and RDF schemas called OIL. One of our main motivations has been to try to ensure that such a proposed standard had a clear and well defined semantics -- a common syntax is useless without an agreement as to what it all means. The core we have currently defined can be justified from both a pragmatic and a theoretical point of view. From a pragmatic point of view, OIL covers consensual modeling primitives of Frame systems and Description Logics. From a theoretical point of view it appears quite natural to us to limit the expressiveness of this version so as to make subsumption decidable. This defines a well-understood subfragment of first-order logic. However, it is important to note that we are open for further discussions that may influence the final design of the language. Clearly future versions will provide variants with more expressive power which lack this reasoning support. Connecting OIL with Horn logic is probably the most challenging question and we will see how far we can get there. We are currently evaluating the use of OIL in the two running IST projects, On-to-knowledge and Ibrow. In On-to-knowledge OIL will be extended to a full-fledged environment for knowledge management in large intranets. Unstructured and semi-structured data will be annotated automatically and agent-based user interface techniques and visualization tools will help user in navigate and query the information space." [cache]

  • See: On-To-Knowledge Project: Content-driven Knowledge-Management through Evolving Ontologies

  • See: - 'Towards a Web Of Meaning...'. Maintained by Stefan Decker (Stanford University). is operated by three research groups: The Onto-Agents and Scalable Knowledge Composition (SKC) Research Group at Stanford University, The Ontobroker-Group at the University of Karlsruhe, and The Protégé Research Group at Stanford University.

  • See: Related 'semantic web' initiatives

  • See: DARPA Agent Mark Up Language (DAML)

  • See: Relational-Functional Markup Language (RFML)

  • See: Ontology and Conceptual Knowledge Markup Languages

  • See: Simple HTML Ontology Extensions (SHOE)

  • See: XOL - XML-Based Ontology Exchange Language

  • See: Case Based Markup Language (CBML)

  • See: Artificial Intelligence Markup Language (AIML)

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