While ‘ontology’ is a branch of philosophy dealing with the nature of things, ‘ontologies’ are formal systems for representing the world in a way that can be used both by people and computers. Ontologies represent the world as what are called ‘entities’ and their ‘properties’; properties consist of ‘relationships’ with other entities.

Entities include things that exist over time such as objects (e.g., human beings) and places (e.g. countries), as well as things that inherently involve change over time such as processes (e.g., behaviour). They can also be characteristics of objects (e.g., age). Relationships can be anything that connects two entities. The most important relationship that every entity should have is the ‘subclass of’ relationship. This tells us what kind of a thing it is. For example, ‘behaviour change intervention’ in BCIO is a subclass of ‘intervention’ which is a subclass of ‘planned process’.

Every entity in an ontology should have a unique ID, a label, a formal definition, and a specification of what it is a subclass of (what we call its ‘parent class’).

With this simple structure we can represent the world in a way that is clear, coherent and consistent by creating a network of entities linked by their relationships.

For a brief introduction go to https://www.ontotext.com/knowledgehub/fundamentals/what-are-ontologies/