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Encyclopedia > Ontology (computer science)

In both computer science and information science, an ontology is a data model that represents a set of concepts within a domain and the relationships between those concepts. It is used to reason about the objects within that domain. Computer science, or computing science, is the study of the theoretical foundations of information and computation and their implementation and application in computer systems. ... The Ancient Library of Alexandria, an early form of information storage and retrieval. ... A data model is a model that describes how data are represented and used in an abstract way. ... The domain of discourse, sometimes called the universe of discourse, is an analytic tool used in deductive logic, especially predicate logic. ... Reasoning is the act of using reason to derive a conclusion from certain premises. ...

Ontologies are used in artificial intelligence, the semantic web, software engineering, biomedical informatics and information architecture as a form of knowledge representation about the world or some part of it. Ontologies generally describe: Garry Kasparov playing against Deep Blue, the first machine to win a chess game against a reigning world champion. ... The semantic web is an evolving extension of the World Wide Web in which web content can be expressed not only in natural language, but also in a form that can be read and used by software agents, thus permitting them to find, share and integrate information more easily. ... Software engineering is the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software. ... Biomedical informatics is a discipline related to bioinformatics and has roots in medical informatics or healthcare informatics. ... This article does not cite any references or sources. ... Knowledge representation is an issue that arises in both cognitive science and artificial intelligence. ...

  • Individuals: the basic or "ground level" objects
  • Classes: sets, collections, or types of objects[1]
  • Attributes: properties, features, characteristics, or parameters that objects can have and share
  • Relations: ways that objects can be related to one another
  • Events: the changing of attributes or relations


Look up class in Wiktionary, the free dictionary. ... In computer science, the set is a collection of certain values without any particular order. ... In computing, attributes are entities that define properties of objects, elements, or files. ... In mathematics, the concept of a relation is a generalization of 2-place relations, such as the relation of equality, denoted by the sign = in a statement like 5 + 7 = 12, or the relation of order, denoted by the sign < in a statement like 5 < 12. Relations that involve two... This page is a candidate for speedy deletion because: this page is a test If you disagree with its speedy deletion, please explain why on its talk page or at Wikipedia:Speedy deletions. ...


Contemporary ontologies share many structural similarities, regardless of the language in which they are expressed. As mentioned above, most ontologies describe individuals (instances), classes (concepts), attributes, and relations. In this section each of these components is discussed in turn.

Individuals (instances)

Individuals (instances) are the basic, "ground level" components of an ontology. The individuals in an ontology may include concrete objects such as people, animals, tables, automobiles, molecules, and planets, as well as abstract individuals such as numbers and words. Strictly speaking, an ontology need not include any individuals, but one of the general purposes of an ontology is to provide a means of classifying individuals, even if those individuals are not explicitly part of the ontology...

Classes (concepts)

Classes (Concepts) are abstract groups, sets, or collections of objects. They may contain individuals, other classes, or a combination of both. Some examples of classes:[2]

  • Person, the class of all people
  • Molecule, the class of all molecules
  • Number, the class of all numbers
  • Vehicle, the class of all vehicles
  • Car, the class of all cars
  • Individual, representing the class of all individuals
  • Class, representing the class of all classes
  • Thing, representing the class of all things
  • Alumna, representing the class of all alumnae
  • Uterus, representing the class of all uteri

Ontologies vary on whether classes can contain other classes, whether a class can belong to itself, whether there is a universal class (that is, a class containing everything), etc. Sometimes restrictions along these lines are made in order to avoid certain well-known paradoxes. Look up paradox in Wiktionary, the free dictionary. ...

The classes of an ontology may be extensional or intensional in nature. A class is extensional if and only if it is characterized solely by its membership. More precisely, a class C is extensional if and only if for any class C', if C' has exactly the same members as C, then C and C' are identical. If a class does not satisfy this condition, then it is intensional. While extensional classes are more well-behaved and well-understood mathematically, as well as less problematic philosophically, they do not permit the fine grained distinctions that ontologies often need to make. For example, an ontology may want to distinguish between the class of all creatures with a kidney and the class of all creatures with a heart, even if these classes happen to have exactly the same members. In Philosophy of language, a context in which a subsentential expression e appears is called extensional iff e can be replaced by an expression with the same extension salva veritate. ... in Philosophy of language: not extensional in Philosophy of mind: An intensional state is a state which has a propositional content. ...

Importantly, a class can subsume or be subsumed by other classes. For example, Vehicle subsumes Car, since (necessarily) anything that is a member of the latter class is a member of the former. The subsumption relation is used to create a hierarchy of classes, typically with a maximally general class like Thing at the top, and very specific classes like 2002 Ford Explorer at the bottom.

A partition is a set of related classes and associated rules that allow objects to be placed into the appropriate class. For example, to the right is the partial diagram of an ontology that has a partition of the Car class into the classes 2-Wheel Drive and 4-Wheel Drive. The partition rule determines if a particular car is placed in the 2-Wheel Drive or the 4-Wheel Drive class. Image File history File links OntologyBasic. ...

If the partition rule(s) guarantee that a single Car cannot be in both classes, then the partition is called a disjoint partition. If the partition rules ensure that every concrete object in the super-class is an instance of at least one of the partition classes, then the partition is called an exhaustive partition.


Objects in the ontology can be described by assigning attributes to them. Each attribute has at least a name and a value, and is used to store information that is specific to the object it is attached to. For example the Ford Explorer object has attributes such as:

  • Name: Ford Explorer
  • Number-of-doors: 4
  • Engine: {4.0L, 4.6L}
  • Transmission: 6-speed

The value of an attribute can be a complex data type; in this example, the value of the attribute called Engine is a list of values, not just a single value. A data type is a constraint placed upon the interpretation of data in a type system in computer programming. ...

If you did not define attributes for the concepts you would have either a taxonomy (if hyponym relationships exist between concepts) or a controlled vocabulary. These are useful, but are not considered true ontologies. They can be pure ontology. Look up taxonomy in Wiktionary, the free dictionary. ... A hyponym (in Greek: υπονύμιον, literally meaning few names) is a word whose extension is included within that of another word. ...

An ontology defines a domain


An important use of attributes is to describe the relationships (also known as relations) between objects in the ontology. Typically a relation is an attribute whose value is another object in the ontology. For example in the ontology that contains the Ford Explorer and the Ford Bronco, the Ford Bronco object might have the following attribute: The Ford Bronco was an SUV produced from 1966 through 1996, with five distinct generations. ...

  • Successor: Ford Explorer

This tells us that the Explorer is the model that replaced the Bronco. Much of the power of ontologies comes from the ability to describe these relations. Together, the set of relations describes the semantics of the domain. The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ...

The most important type of relation is the subsumption relation (is-superclass-of, the converse of is-a, is-subtype-of or is-subclass-of). This defines which objects are members of classes of objects. For example we have already seen that the Ford Explorer is-a 4-wheel drive, which in turn is-a Car: Symbolic Logic - See minor premise Object-Oriented Programming - See Liskov Substitution Principle ... In biology, a superclass is a taxonomic grade intermediate between subphylum and class. ... In computer science, the term inheritance may be applied to a variety of situations in which certain characteristics are passed on from one context to another. ... In object-oriented programming, subclass is a class that is derived from another class or classes. ...

The addition of the is-a relationships has created a hierarchical taxonomy; a tree-like structure (or, more generally, a partially ordered set) that clearly depicts how objects relate to one another. In such a structure, each object is the 'child' of a 'parent class' (Some languages restrict the is-a relationship to one parent for all nodes, but many do not). Image File history File links OntologyBronco. ... Look up taxonomy in Wiktionary, the free dictionary. ... In mathematics, especially order theory, a partially ordered set (or poset) is a set equipped with a partial order relation. ...

Another common type of relations is the meronymy relation, written as part-of, that represents how objects combine together to form composite objects. For example, if we extended our example ontology to include objects like Steering Wheel, we would say that "Steering Wheel is-part-of Ford Explorer" since a steering wheel is one of the components of a Ford Explorer. If we introduce meronymy relationships to our ontology, we find that this simple and elegant tree structure quickly becomes complex and significantly more difficult to interpret manually. It is not difficult to understand why; an entity that is described as 'part of' another entity might also be 'part of' a third entity. Consequently, entities may have more than one parent. The structure that emerges is known as a directed acyclic graph (DAG). Meronymy (from the Greek words meros = part and onoma = name) is a semantic relation. ... A simple directed acyclic graph In computer science and mathematics, a directed acyclic graph, also called a dag or DAG, is a directed graph with no directed cycles; that is, for any vertex v, there is no nonempty directed path that starts and ends on v. ...

As well as the standard is-a and part-of relations, ontologies often include additional types of relation that further refine the semantics they model. These relations are often domain-specific and are used to answer particular types of question.

For example in the domain of automobiles, we might define a made-in relationship which tells us where each car is built. So the Ford Explorer is made-in Louisville. The ontology may also know that Louisville is-in Kentucky and Kentucky is-a state of the USA. Software using this ontology could now answer a question like "which cars are made in America?" “Louisville” redirects here. ... Official language(s) English[1] Capital Frankfort Largest city Louisville Area  Ranked 37th  - Total 40,444 sq mi (104,749 km²)  - Width 140 miles (225 km)  - Length 379 miles (610 km)  - % water 1. ...

Domain ontologies and upper ontologies

A domain ontology (or domain-specific ontology) models a specific domain, or part of the world. It represents the particular meanings of terms as they apply to that domain. For example the word card has many different meanings. An ontology about the domain of poker would model the "playing card" meaning of the word, while an ontology about the domain of computer hardware would model the "punch card" and "video card" meanings. Look up card in Wiktionary, the free dictionary. ... A game of Texas holdem, currently the most popular form of poker, in progress. ... This article needs additional references or sources for verification. ... Computer hardware is the physical part of a computer, including the digital circuitry, as distinguished from the computer software that executes within the hardware. ... Punched cards (or Hollerith cards, or IBM cards), are pieces of stiff paper that contain digital information represented by the presence or absence of holes in predefined positions. ... A video card, (also referred to as a graphics accelerator card, display adapter, graphics card, and numerous other terms), is an item of personal computer hardware whose function is to generate and output images to a display. ...

An upper ontology (or foundation ontology) is a model of the common objects that are generally applicable across a wide range of domain ontologies. It contains a core glossary in whose terms objects in a set of domains can be described. There are several standardized upper ontologies available for use, including Dublin Core, GFO, OpenCyc/ResearchCyc, SUMO, and DOLCEl. WordNet, while considered an upper ontology by some, is not an ontology: it is a unique combination of a taxonomy and a controlled vocabulary (see above, under Attributes). To meet Wikipedias quality standards, this article or section may require cleanup. ... A core glossary is a simple glossary or defining dictionary which enables definition of other concepts, especially for newcomers to a language or field of study. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... The General Formal Ontology (GFO) is an upper ontology integrating processes and objects. ... Cyc is an artificial intelligence project which attempts to assemble a comprehensive ontology and database of everyday common-sense knowledge, with the goal of enabling AI applications to perform human-like reasoning. ... Cyc is an artificial intelligence project which attempts to assemble a comprehensive ontology and database of everyday common-sense knowledge, with the goal of enabling AI applications to perform human-like reasoning. ... It has been suggested that SUMO class be merged into this article or section. ... WordNet is a semantic lexicon for the English language. ... Look up taxonomy in Wiktionary, the free dictionary. ...

Since domain ontologies represent concepts in very specific and often eclectic ways, they are often incompatible. As systems that rely on domain ontologies expand, they often need to merge domain ontologies into a more general representation. This presents a challenge to the ontology engineer. Different ontologies in the same domain can also arise due to different perceptions of the domain based on cultural background, education, ideology, or because a different representation language was chosen.

At present, merging ontologies is a largely manual process and therefore time-consuming and expensive. Using a foundation ontology to provide a common definition of core terms can make this process manageable. There are studies on generalized techniques for merging ontologies, but this area of research is still largely theoretical.

Ontology languages

An ontology language is a formal language used to encode the ontology. There are a number of such languages for ontologies, both proprietary and standards-based: In mathematics, logic, and computer science, a formal language is a language that is defined by precise mathematical or machine processable formulas. ...

  • OWL is a language for making ontological statements, developed as a follow-on from RDF and RDFS, as well as earlier ontology language projects including OIL, DAML and DAML+OIL. OWL is intended to be used over the World Wide Web, and all its elements (classes, properties and individuals) are defined as RDF resources, and identified by URIs.
  • KIF is a syntax for first-order logic that is based on S-expressions.
  • The Cyc project has its own ontology language called CycL, based on first-order predicate calculus with some higher-order extensions.
  • Rule Interchange Format (RIF) and F-Logic combine ontologies and rules.

The Web Ontology Language (OWL) is a language for defining and instantiating Web ontologies. ... Resource Description Framework (RDF) is a family of World Wide Web Consortium (W3C) specifications originally designed as a metadata model but which has come to be used as a general method of modeling information, through a variety of syntax formats. ... ... OIL (Ontology Inference Layer or Ontology Interchange Language) can be regarded as an Ontology infrastructure for the Semantic Web (see paper OIL: An Ontology Infrastructure for the Semantic Web, IEEE Intelligent Systems, March/April 2001). ... The DARPA Agent Markup Language (DAML) is a agent markup language developed by the Defense Advanced Research Projects Agency (DARPA) for the semantic web. ... A succesor language to DAML and OIL that combines features of both. ... WWWs historical logo designed by Robert Cailliau The World Wide Web is a system of interlinked, hypertext documents accessed via the Internet. ... The term resource is a foundational term in World Wide Web architecture because it is the root of Uniform Resource Identifiers, also known as URIs and URLs. ... A Uniform Resource Identifier (URI), is a compact string of characters used to identify or name a resource. ... Knowledge Interchange Format was created to serve as a syntax for first order logic that is easy for computers to process. ... First-order logic (FOL) is a universal language in symbolic science, and is in use everyday by mathematicians, philosophers, linguists, computer scientists and practitioners of artificial intelligence. ... An S-expression (S stands for symbolic) is a convention for representing data or an expression in a computer program in a text form. ... Cyc is an artificial intelligence project that attempts to assemble a comprehensive ontology and database of everyday common sense knowledge, with the goal of enabling AI applications to perform human-like reasoning. ... CycL was originally a frame language used by Doug Lenats Cyc Artificial Intelligence project. ... First-order predicate calculus or first-order logic (FOL) permits the formulation of quantified statements such as there exists an x such that. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... F-logic (frame logic) is a knowledge representation- and ontology language. ...

Relation to the philosophical term

The term ontology has its origin in philosophy, where it is the name of one fundamental branch of metaphysics, concerned with analyzing various types or modes of existence, often with special attention to the relations between particulars and universals, between intrinsic and extrinsic properties, and between essence and existence. According to Tom Gruber at Stanford University, the meaning of ontology in the context of computer science is “a description of the concepts and relationships that can exist for an agent or a community of agents.” He goes on to specify that an ontology is generally written, “as a set of definitions of formal vocabulary.” [3] In philosophy, ontology (from the Greek , genitive : of being (part. ... Plato (Left) and Aristotle (right), by Raphael (Stanza della Segnatura, Rome) Metaphysics is the branch of philosophy concerned with explaining the ultimate nature of reality, being, and the world. ... Leland Stanford Junior University, commonly known as Stanford University (or simply Stanford), is a private university located approximately 37 miles (60 kilometers) southeast of San Francisco and approximately 20 miles northwest of San José in Stanford, California. ... In computer science, a software agent is an abstraction, a logical model that describes software that acts for a user or other program in a relationship of agency. ...

What ontology has in common in both computer science and philosophy is the representation of entities, ideas, and events, along with their properties and relations, according to a system of categories. In both fields, one finds considerable work on problems of ontological relativity (e.g. Quine and Kripke in philosophy, Sowa and Guarino in computer science[citation needed]), and debates concerning whether a normative ontology is viable (e.g. debates over foundationalism in philosophy, debates over the Cyc project in AI). Cyc is an artificial intelligence project that attempts to assemble a comprehensive ontology and database of everyday common sense knowledge, with the goal of enabling AI applications to perform human-like reasoning. ...

Differences between the two are largely matters of focus. Philosophers are less concerned with establishing fixed, controlled vocabularies than are researchers in computer science, while computer scientists are less involved in discussions of first principles (such as debating whether there are such things as fixed essences, or whether entities must be ontologically more primary than processes). During the second half of the 20th century, philosophers extensively debated the possible methods or approaches to building ontologies, without actually building any very elaborate ontologies themselves. By contrast, computer scientists were building some large and robust ontologies (such as WordNet and Cyc) with comparatively little debate over how they were built. WordNet is a semantic lexicon for the English language. ... Cyc is an artificial intelligence project that attempts to assemble a comprehensive ontology and database of everyday common sense knowledge, with the goal of enabling AI applications to perform human-like reasoning. ...

In the early years of the 21st century, the interdisciplinary project of cognitive science has been bringing the two circles of scholars closer together. For example, there is talk of a "computational turn in philosophy" which includes philosophers analyzing the formal ontologies of computer science (sometimes even working directly with the software), while researchers in computer science have been making more references to those philosophers who work on ontology (sometimes with direct consequences for their methods). Still, many scholars in both fields are uninvolved in this trend of cognitive science, and continue to work independently of one another, pursuing separately their different concerns.


Examples of published ontologies

The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... Cyc is an artificial intelligence project that attempts to assemble a comprehensive ontology and database of everyday common sense knowledge, with the goal of enabling AI applications to perform human-like reasoning. ... It has been suggested that SUMO class be merged into this article or section. ... WordNet is a semantic lexicon for the English language. ... The Gene Ontology, or GO, project can be broadly split into two parts. ... Genomics is the study of an organisms entire genome; Rathore et al, . Investigation of single genes, their functions and roles is something very common in todays medical and biological research, and cannot be said to be genomics but rather the most typical feature of molecular biology. ... This article or section is in need of attention from an expert on the subject. ... SBO is the Systems Biology Ontology project, another cornerstone of the BioModels. ... CIDOC is the Committee on Documentation of the International Council of Museums (ICOM). ... Cultural heritage (national heritage or just heritage) is the legacy of physical artifacts and intangible attributes of a group or society that are inherited from past generations, maintained in the present and bestowed for the benefit of future generations. ... This article does not cite its references or sources. ... ThoughtTreasure is a commonsense knowledge base and architecture for natural language processing. ... LPL can mean Linsco/Private Ledger Financial Services, an organization of independent financial advisors Lipoprotein lipase, an enzyme which hydrolyzes lipids in lipoproteins Liverpool John Lennon Airport, IATA airport code Lunar and Planetary Laboratory Department of the University of Arizona LPL an autosomal gene. ... TIME-ITEM is an ontology of Topics that describes the content of undergraduate medical education. ...

Ontology libraries

The development of ontologies for the Web has led to the apparition of services providing lists or directories of ontologies with search facility. Such directories have been called ontology libraries.

The following are static libraries of human-selected ontologies.

  • The DAML Ontology Library maintains a legacy of ontologies in DAML.
  • SchemaWeb is a directory of RDF schemas expressed in RDFS, OWL and DAML+OIL.

The following are both directories and search engines. They include crawlers searching the Web for well-formed ontologies.

  • Swoogle is a directory and search engine for all RDF resources available on the Web, including ontologies.
  • The OntoSelect Ontology Library offers similar services for RDF/S, DAML and OWL ontologies.
  • Ontaria is a "searchable and browsable directory of semantic web data", with a focus on RDF vocabularies with OWL ontologies.

Swoogle is a search engine for Semantic Web documents, terms and data found on the Web. ...


  1. ^ See Class (set theory), Class (computer science), and Class (philosophy), each of which is relevant but not identical to the notion of a "class" here.
  2. ^ Note that the names given to the classes mentioned here are entirely a matter of convention.
  3. ^ http://www-ksl.stanford.edu/kst/what-is-an-ontology.html

In set theory and its applications throughout mathematics, a class is a collection of sets (or sometimes other mathematical objects) that can be unambiguously defined by a property that all its members share. ... In object-oriented programming, a class is a programming language construct that is used to group related instance variables and methods. ... Philosophers sometimes distinguish classes from types and kinds. ...

See also

Related philosophical concepts: The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... Open Biomedical Ontologies (formerly Open Biological Ontologies) is an effort to create controlled vocabularies for shared use across different biological and medical domains. ... Ontology Alignment is the process of determining correspondences between concepts. ... Controlled vocabularies are used in indexing schemes, subject headings, thesauri and taxonomies. ... A concept lattice for objects consisting of the integers from 1 to 10, and attributes composite, even, odd, prime, and square. ... Terminology extraction, term extraction, or glossary extraction, is a subtask of information extraction. ... Ontology learning [1], ontology extraction, ontology generation, or ontology acquisition, is a subtask of information extraction. ... Ontology editors are applications designed to assist in the creation or manipulation of ontologies. ... Soft Ontology, coined by Eli Hirsch in 1993, refers to the embracing or reconciling of apparent ontological differences by means of relevant distinctions and contextual analyses. ... The name lattice is suggested by the form of the Hasse diagram depicting it. ...

The Natural Semantic Metalanguage (NSM) is an approach to semantic analysis based on reductive paraphrase (that is, breaking concepts/words down into combinations of simpler concepts/words, see oligosynthetic) using a small collection of semantic primes. ... Characteristica Universalis from Latin is commonly interpreted as Universal Character in English. ... The idea of an alphabet of human thought originates in the 17th century, when proposals were first made for a universal language. ... In logic and linguistics, a metalanguage is a language used to make statements about other languages (object languages). ...

External links

  • What is an ontology?
  • Introduction to Description Logics DL course by Enrico Franconi, Faculty of Computer Science, Free University of Bolzano, Italy
  • What are the differences between a vocabulary, a taxonomy, a thesaurus, an ontology, and a meta-model?
  • Clay Shirky: Ontology is Overrated
  • Ontolog (a.k.a. Ontolog Forum) - An open, international, virtual community of practice working on the application and adoption of ontological engineering and semantic technologies.
  • Barry Smith's Ontology Page
  • John Bateman's Ontology Portal
  • Buffalo Ontology Site
  • National Center for Ontological Research
  • National Center for Biomedical Ontology
  • Bremen Ontology Research Group
  • The OBO Foundry
  • The Laboratory for Applied Ontology (LOA)
  • ekoss.org - Expert Knowledge Ontology-based Semantic Search
  • Streaming video: "How to Build an Ontology", by Barry Smith.
  • Jena – A Semantic Web Framework for Java
  • Soft ontologies

  Results from FactBites:
Ontology (computer science) - Wikinfo (2281 words)
In computer science, an ontology is the attempt to formulate an exhaustive and rigorous conceptual schema within a given domain, a typically hierarchical data structure containing all the relevant entities and their relationships and rules (theorems, regulations) within that domain.
The purpose of a computational ontology is not to specify what does or does not 'exist', but to create a database, which is a human artifact, containing concepts referring to entities of interest to the ontologist, and which will be useful in performing certain types of computations.
Computer programs can use an ontology for a variety of purposes including inductive reasoning, classification, a variety of problem solving techniques, as well as to facilitate communication and sharing of information between different systems.
  More results at FactBites »



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