Ontologies resemble class hierarchies in object-oriented programming but there are several critical differences.
Class hierarchies are meant to represent structures used in source code that evolve fairly slowly (perhaps with monthly revisions) whereas ontologies are meant to represent information on the Internet and are expected to be evolving almost constantly.
Similarly, ontologies are typically far more flexible as they are meant to represent information on the Internet coming from all sorts of heterogeneous data sources.
Class hierarchies on the other hand tend to be fairly static and rely on far less diverse and more structured sources of data such as corporate databases.
They are built upon the World Wide Web Consortium's (W3C) standard for objects called the Resource Description Framework (RDF).
[11] The OWL family contains many species, serializations, syntaxes and specifications with similar names.
Since the 1990s, a number of research efforts have explored how the idea of knowledge representation (KR) from artificial intelligence (AI) could be made useful on the World Wide Web.
In 2000 in the United States, DARPA started development of DAML led by James Hendler.
[15][self-published source] In March 2001, the Joint EU/US Committee on Agent Markup Languages decided that DAML should be merged with OIL.
DAML+OIL was intended to be a thin layer above RDFS,[15] with formal semantics based on a description logic (DL).
[17] The Semantic Web provides a common framework that allows data to be shared and reused across application, enterprise, and community boundaries.a declarative representation language influenced by ideas from knowledge representationIn the late 1990s, the World Wide Web Consortium (W3C) Metadata Activity started work on RDF Schema (RDFS), a language for RDF vocabulary sharing.
[21][self-published source] As of Monday, the 31st of May, our working group will officially come to an end.
[22] In 2005, at the OWL Experiences And Directions Workshop a consensus formed that recent advances in description logic would allow a more expressive revision to satisfy user requirements more comprehensively whilst retaining good computational properties.
The W3C chartered the OWL Working Group as part of the Semantic Web Activity in September 2007.
[6][25] Why not be inconsistent in at least one aspect of a language which is all about consistency?OWL was chosen as an easily pronounced acronym that would yield good logos, suggest wisdom, and honor William A. Martin's One World Language knowledge representation project from the 1970s.
[17] An ontology describing families might include axioms stating that a "hasMother" property is only present between two individuals when "hasParent" is also present, and that individuals of class "HasTypeOBlood" are never related via "hasParent" to members of the "HasTypeABBlood" class.
OWL Lite was originally intended to support those users primarily needing a classification hierarchy and simple constraints.
It was hoped that it would be simpler to provide tool support for OWL Lite than its more expressive relatives, allowing quick migration path for systems using thesauri and other taxonomies.
[24] OWL DL is designed to provide the maximum expressiveness possible while retaining computational completeness (either φ or ¬φ holds), decidability (there is an effective procedure to determine whether φ is derivable or not), and the availability of practical reasoning algorithms.
High level syntax is used to specify the OWL ontology structure and semantics.
[34] The OWL abstract syntax presents an ontology as a sequence of annotations, axioms and facts.
Information about the classes, properties and individuals that compose the ontology is contained in axioms and facts only.
This style is similar to frame languages, and quite dissimilar to well known syntaxes for DLs and Resource Description Framework (RDF).
Today, however, there are almost as many meanings for this inheritance link as there are knowledge-representation systems.Early attempts to build large ontologies were plagued by a lack of clear definitions.
Members of the OWL family have model theoretic formal semantics, and so have strong logical foundations.
[44] They combine a syntax for describing and exchanging ontologies, and formal semantics that gives them meaning.
[45] Sound, complete, terminating reasoners (i.e. systems which are guaranteed to derive every consequence of the knowledge in an ontology) exist for these DLs.