In its original meaning, ontology refers to the study of the essence of everything that exists in the universe. However, in computer science, the definition of ontology is: “an explicit and formal specification of a shared concept.” In this definition, the word “shared” indicates that concepts within the ontology are based upon the knowledge that each computer has approved. In simpler terms, an ontology is the clear expression of a given knowledge or information in a previously-defined format, so that several computers can share the information.
Ontology is composed of concepts and the relationships between the concepts. A concept refers to a fundamental meaningful unit. For example, ‘a man’ and ‘a building’ are concepts. A relationship refers to the interrelationship formed between concepts. For example, ‘a man lives in a building’ can be expressed as the relationship ‘to live’ formed in between the concepts ‘a man’ and ‘a building’.