Introduction to Ontologies

OWL is built on RDFS which helps us to define ontologies.
Ontologies are formal definitions of vocabularies that allow us to define difficult or complex structures and new relationships between vocabulary terms and members of classes that we define. Ontologies generally describe specific domains such as scientific research areas.

Example:
Ontology depicting Movie:-

Components:

1. Individuals –
   Individuals are also known as instances of objects or concepts.It may or may not be present in an ontology.It represents the atomic level of an ontology.

   For example, in the above ontology of movie, individuals can be a film (Titanic), a director (James Cameron), an actor (Leonardo DiCaprio).

2. Classes –
   Sets of collections of various objects are termed as classes.

   For example, in the above ontology representing movie, movie genre (e.g. Thriller, Drama), types of person (Actor or Director) are classes.

3. Attributes –
   Properties that objects may possess.

   For example, a movie is described by the set of ‘parts’ it contains like Script, Director, Actors.

4. Relations –
   Ways in which concepts are related to one another.

   For example, as shown above in the diagram a movie has to have a script and actors in it.

Different Ontology Languages:

• CycL – It was developed for the Cyc project and is based on First Order Predicate Calculus.
• Rule Interchange Format (RIF) – It is the language used for combining ontologies and rules.
• Open Biomedical Ontologies (OBO) – It is used for various biological and biomedical ontologies.
• Web Ontology Language (OWL) – It is developed for using ontologies over the World Wide Web (WWW).