An ontology is defined as a formal framework that establishes concepts, categories, and their relationships within a specific domain. It serves as an abstract and conceptual blueprint, providing the necessary schema and rules for standardizing and interpreting data, enabling semantic consistency and automated reasoning across different systems. For example, in the finance domain, an ontology might define concepts like “Bank,” “Account,” and “Transaction”.
Ontologies play a critical structural role relative to Knowledge Graphs (KGs). They are referred to as the Organizing Principles—the rules and philosophical structure—upon which the Knowledge Graph is built. While the KG is a concrete, data-driven network of actual entities and relationships, the ontology defines the possibilities and constraints for those entities.
The purpose of an ontology is profound: it ensures domain understanding and logical consistency, facilitating data integration, semantic interoperability, and domain modeling. By defining the boundaries and relationships within a topic, ontologies provide the foundation for search engines to perform advanced functions like entity disambiguation and contextual query interpretation.