In computer science

Computer science

Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...

 and artificial intelligence

Artificial intelligence

Artificial intelligence is the intelligence of machines and the branch of computer science that aims to create it. AI textbooks define the field as "the study and design of intelligent agents" where an intelligent agent is a system that perceives its environment and takes actions that maximize its...

, ontology languages are formal language

Formal language

A formal language is a set of words—that is, finite strings of letters, symbols, or tokens that are defined in the language. The set from which these letters are taken is the alphabet over which the language is defined. A formal language is often defined by means of a formal grammar...

s used to construct ontologies. They allow the encoding of knowledge

Knowledge

Knowledge is a familiarity with someone or something unknown, which can include information, facts, descriptions, or skills acquired through experience or education. It can refer to the theoretical or practical understanding of a subject...

 about specific domains and often include reasoning rules that support the processing of that knowledge. Ontology languages are usually declarative languages, are almost always generalizations of frame language

Frame language

A frame language is a metalanguage. It applies the frame concept to the structuring of language properties. Frame languages are usually software languages.-Description:...

s, and are commonly based on either first-order logic

First-order logic

First-order logic is a formal logical system used in mathematics, philosophy, linguistics, and computer science. It goes by many names, including: first-order predicate calculus, the lower predicate calculus, quantification theory, and predicate logic...

 or on description logic

Description logic

Description logic is a family of formal knowledge representation languages. It is more expressive than propositional logic but has more efficient decision problems than first-order predicate logic....

.

Traditional ontology languages

• Common Logic
  Common logic
  Common logic is a framework for a family of logic languages, based on first-order logic, intended to facilitate the exchange and transmission of knowledge in computer-based systems....
  
   - and its dialects
• CycL
  CycL
  CycL in computer science and artificial intelligence is an ontology language used by Doug Lenat's Cyc artificial intelligence project. Ramanathan V. Guha was instrumental in the design of early versions of the language. There is a close variant of CycL known as MELD.The original version of CycL was...
  
  
• DOGMA
  DOGMA
  DOGMA, short for Developing Ontology-Grounded Methods and Applications, is the name of research project in progress at Vrije Universiteit Brussel's STARLab, Semantics Technology and Applications Research Laboratory...
  
   (Developing Ontology-Grounded Methods and Applications)
• F-Logic
  F-logic
  F-logic is a knowledge representation- and ontology language. F-logic combines the advantages of conceptual modeling with object-oriented, frame-based languages and offers a declarative, compact and simple syntax, as well as the well-defined semantics of a logic-based language.Features include,...
  
   (Frame Logic)
• KIF
  Knowledge Interchange Format
  Knowledge Interchange Format is a computer-oriented language for the interchange of knowledge among disparate computer programs.It has declarative semantics ; it is logically comprehensive Knowledge Interchange Format (KIF) is a computer-oriented language for the interchange of knowledge among...
  
   (Knowledge Interchange Format)
  • Ontolingua based on KIF
• KL-ONE
  KL-ONE
  KL-ONE is a well known knowledge representation system in the tradition of semantic networks and frames; that is, it is a frame language. The system is an attempt to overcome semantic indistinctness in semantic network representations and to explicitly represent conceptual information as a...
  
  
• KM programming language
  KM programming language
  KM, the Knowledge Machine, is a frame-based language used for knowledge representation work.It has first-order logic semantics, and includes machinery for reasoning, including selection by description, unification, classification, and reasoning about actions...
  
  
• LOOM (ontology)
  LOOM (ontology)
  Loom or LOOM is a knowledge representation language developed by researchers in the Artificial Intelligence research group at the University of Southern California's Information Sciences Institute...
  
  
• OCML
  OCML
  Open Configuration and Management Layer is a universal application configuration and management layer that helps to develop integrated applications independent of underlying group of applications, configurations and management....
  
   (Operational Conceptual Modelling Language)
• OKBC (Open Knowledge Base Connectivity
  Open Knowledge Base Connectivity
  Open Knowledge Base Connectivity is a protocol and an API for accessing knowledge in knowledge representation systems such as ontology repositories and object-relational databases. It is somewhat complementary to the Knowledge Interchange Format that serves as a general representation language...
  
  )
• PLIB (Parts LIBrary)
• RACER

Markup ontology languages

These languages use a markup

Markup language

A markup language is a modern system for annotating a text in a way that is syntactically distinguishable from that text. The idea and terminology evolved from the "marking up" of manuscripts, i.e. the revision instructions by editors, traditionally written with a blue pencil on authors' manuscripts...

 scheme to encode knowledge, most commonly with XML

XML

Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....

.

• DAML+OIL
• Ontology Inference Layer
  Ontology Inference Layer
  OIL can be regarded as an Ontology infrastructure for the Semantic Web. OIL is based on concepts developed in Description Logic and frame-based systems and is compatible with RDFS....
  
   (OIL)
• Web Ontology Language
  Web Ontology Language
  The Web Ontology Language is a family of knowledge representation languages for authoring ontologies.The languages are characterised by formal semantics and RDF/XML-based serializations for the Semantic Web...
  
   (OWL)
• Resource Description Framework
  Resource Description Framework
  The Resource Description Framework is a family of World Wide Web Consortium specifications originally designed as a metadata data model...
  
   (RDF)
• RDF Schema
  RDF Schema
  RDF Schema is a set of classes with certain properties using the RDF extensible knowledge representation language, providing basic elements for the description of ontologies, otherwise called RDF vocabularies, intended to structure RDF resources...
  
  
• SHOE
  Simple HTML Ontology Extensions
  In the semantic web, Simple HTML Ontology Extensions are a small set of HTML extensions designed to give web pages semantic meaning by allowing information such as class, subclass and property relationships....
  
  

Frame-based

F-Logic, OKBC, and KM

KM programming language

KM, the Knowledge Machine, is a frame-based language used for knowledge representation work.It has first-order logic semantics, and includes machinery for reasoning, including selection by description, unification, classification, and reasoning about actions...

 are completely or partially frame-based languages.

Description logic-based

Description logic

Description logic

Description logic is a family of formal knowledge representation languages. It is more expressive than propositional logic but has more efficient decision problems than first-order predicate logic....

 provides an extension of frame language

Frame language

A frame language is a metalanguage. It applies the frame concept to the structuring of language properties. Frame languages are usually software languages.-Description:...

s, without going so far as to take the leap to first-order logic

First-order logic

First-order logic is a formal logical system used in mathematics, philosophy, linguistics, and computer science. It goes by many names, including: first-order predicate calculus, the lower predicate calculus, quantification theory, and predicate logic...

 and support for arbitrary predicates. Examples include KL-ONE

KL-ONE

KL-ONE is a well known knowledge representation system in the tradition of semantic networks and frames; that is, it is a frame language. The system is an attempt to overcome semantic indistinctness in semantic network representations and to explicitly represent conceptual information as a...

, RACER, and OWL

Web Ontology Language

The Web Ontology Language is a family of knowledge representation languages for authoring ontologies.The languages are characterised by formal semantics and RDF/XML-based serializations for the Semantic Web...

.

Gellish

Gellish

Gellish is a controlled natural language, also called a formal language, in which information and knowledge can be expressed in such a way that it is computer-interpretable, as well as system-independent. Gellish is a structured subset of natural language that is suitable for information modelling...

 is an example of a combined ontology language and ontology that is description logic based. It distinguishes between the semantic differences among others of:

• relation types for relations between concepts (classes)
• relation types for relations between individuals
• relation types for relations between individuals and classes

It also contains constructs to express queries and communicative intent.

First-order logic-based

Common Logic

Common logic

Common logic is a framework for a family of logic languages, based on first-order logic, intended to facilitate the exchange and transmission of knowledge in computer-based systems....

, CycL

CycL

CycL in computer science and artificial intelligence is an ontology language used by Doug Lenat's Cyc artificial intelligence project. Ramanathan V. Guha was instrumental in the design of early versions of the language. There is a close variant of CycL known as MELD.The original version of CycL was...

 and KIF

Knowledge Interchange Format

Knowledge Interchange Format is a computer-oriented language for the interchange of knowledge among disparate computer programs.It has declarative semantics ; it is logically comprehensive Knowledge Interchange Format (KIF) is a computer-oriented language for the interchange of knowledge among...

 are examples of languages that support expressions in first-order logic

First-order logic

First-order logic is a formal logical system used in mathematics, philosophy, linguistics, and computer science. It goes by many names, including: first-order predicate calculus, the lower predicate calculus, quantification theory, and predicate logic...

, and, in particular, allow general predicates.

See also

• Formal concept analysis
  Formal concept analysis
  Formal concept analysis is a principled way of automatically deriving an ontology from a collection of objects and their properties. The term was introduced by Rudolf Wille in 1984, and builds on applied lattice and order theory that was developed by Birkhoff and others in the 1930s.-Intuitive...
  
  
• Lattice (order)
  Lattice (order)
  In mathematics, a lattice is a partially ordered set in which any two elements have a unique supremum and an infimum . Lattices can also be characterized as algebraic structures satisfying certain axiomatic identities...
  
  
• Domain theory
  Domain theory
  Domain theory is a branch of mathematics that studies special kinds of partially ordered sets commonly called domains. Consequently, domain theory can be considered as a branch of order theory. The field has major applications in computer science, where it is used to specify denotational...
  
  
• Galois connection
  Galois connection
  In mathematics, especially in order theory, a Galois connection is a particular correspondence between two partially ordered sets . The same notion can also be defined on preordered sets or classes; this article presents the common case of posets. Galois connections generalize the correspondence...