Ontologies in Semantic Web

I mentioned about Social Semantic Web on my blog earlier. We had a brief introduction to the Social Semantic Web there. Now I would like to touch upon the concept of ontology which is frequently used in Social Semantic Web.

Ontology is the base of the Semantic Web. It represents the conceptualization of a specific domain that is shared by a community of users and defined in a machine-readable language to share the semantic information between explicitly automated systems. It is a relevant research issue depending on the extraction of information from the web [1].

Ontology can be applied to create a knowledge graph in which types and their relationships are expressed by nodes and edges.

Picture 1. The ontology graph of a well-known ontology named Travel

Ontologies are constructed by using some ontology supporting languages like RDF, OWL, etc. OWL is a semantic web computational logic-based language designed to represent rich and complex information about objects and their relationships. OWL specifies object classes, relationship properties, hierarchical order and enriches ontology modeling in semantic graph databases, also known as RDFs [2].

Most ontologies describe individuals (instances), classes (concepts), attributes and relations. The common components of ontologies include [3]:

• Classes (sets, collections, concepts, classes in programming)
• Individuals (instances or objects from classes)
• Properties (attributes or parameters of objects)
• Relations (paths betwen classes and individuals can be related to one another)
• Restrictions (formally stated descriptions, constraints)
• Rules (statements that make up logical inferences that can be drawn from a particular claim)
• Events (the changing of attributes or relations)
• Axioms (assertions in logical form containing the general theory defined by ontology)

Picture 2 shows the data of the well-known Travel ontology and the diagram of the relationship between them.

Picture 2. Some classes, instances, and relations among them in the Travel domain

Why do we need to develop an ontology?

Ontologies are used for creating a common understanding of the structure of information among people or software agents. Ontologies are important for reusing and analyzing the domain knowledge and making some inferences about the domain.

Ontology Editors

The tools that can be used to examine existing ontologies or to create a new ontology are as follows:

• Protégé
• NeOn Toolkit
• SWOOP
• Neologism
• Knoodl

In my next blog post, I will talk about the use of Protégé which is an ontology editor by developed by Stanford University.

References

[1] Zeeshan Ahmed and Detlef Gerhard, “Role of Ontology in Semantic Web Development”
[2] Ontotext, “What are Ontologies?”
[3] Wikipedia, “Ontology (information science)”