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Ontology is a model of organized knowledge in a restricted domain. It refers to the representation of various concepts and the relationships between these concepts. In computer science terms, ontology is defined as “an explicit specification of conceptualization” [5].

The components of ontology are individuals, classes, attributes and relationships. In ontology, concepts refer to objects, which will be organized, attributes are the traits of the objects, relationships connect two concepts and instances are the actual data in an information system [7].

Components of ontology: [8] The components of ontology are

1. Individuals
2. Classes
3. Attributes
4. Relationships

  • Individuals:

Individuals are also referred to as instances. They are the basic “ground level” components of 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.

  • Classes:

Classes are also referred to as concepts. Concepts are type, sort, category which include the abstract groups, sets and collection of objects. Ontologies vary based on whether a class can contain other class or whether a class can belong to itself.

A class can be subsumed to another classes which is called as a subclass. The subsumption relation creates hierarchy of classes. The parent class is the subsuming class and the subclass is the subsumed class. The subsumed class (subclass) inherits the properties from the subsuming class (parent class). This means, anything that is necessarily true about the parent class must be necessarily true in a subsumed child class. In ontologies, the class which has a single parent is considered as single inheritance where as if a class has many parents it is considered as multiple inheritances. In multiple inheritances all necessary properties of the subsuming classes are inherited by subsumed class.

  • Attributes:

Attributes are used to describe an object. The attributes have a name and a value.and is used to store information that is specific to the object.

  • Relationships:

Relation connects two concepts or an object to a property. The most important relation in ontology is the subsumption relation which includes “is-super class-of, is-subclass-of” and others. This defines which objects are members of class of objects. The is-a relationship creates hierarchical taxonomy, a tree like structure that clearly shows how objects are related to each other. Another type of relation is “part-of”, which represents how objects are combined to form composite objects.

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Key points
  • Ontology increases the efficiency and consistency of describing resources, by enabling functionalities in development of knowledge management and information retrieval applications [7].
  • The languages such as Resource Description Framework [11], RDF Schema [12] and Web Ontology Language [9], provide structures for sharing common descriptions, definitions and relations within the agricultural community.

5) Gruber T. (1993), A translation approach to portable ontology specifications, Knowledge Acquisition 5:199-220
7) Margherita Sini, Gauri Salokhe, Christopher Pardy, Janica Albert, Johannes Keizer, Stephen Katz (2007), Ontology based Navigation of Bibliographic Metadata: Example from the Food, Nutrition and Agriculture Journal; Food and Agriculture Organization of the United Nations, Rome, Italy URL:http://drtc.isibang.ac.in/sdl/index.php/record/view/283
8) Oscar Corcho1, Asunción Gómez-Pérez1, A Roadmap to Ontology Specification Languages, 12th International Conference on Knowledge Engineering and Knowledge Management
9) OWL Web Ontology Language (2004). Retrieved January 23, 2006, from URL:http://www.w3.org/TR/owl-features/
11) RDF Primer (2004). Retrieved January 23, 2006, from URL:http://www.w3.org/RDF/
12) RDF Vocabulary Description Language 1.0: RDF Schema (2004). Retrieved January 23, 2006, from URL:http://www.w3.org/TR/rdf-schema/