In computer science, the term ontology refers to a “formal, explicit specification of a shared conceptualization” [ 1 ]. Conceptualization refers to an abstract model that allows describing something relevant in the world, for which we normally use concepts, properties and constraints on their application (for instance, the Unified Modeling Language [UML] class diagrams that many software developers use, the entity-relationship models used to organize a database or any drawing that one makes in a whiteboard to start organizing an information model for system development). All those entities in the abstract model need to be described explicitly so that we cover as much as possible of the world phenomenon that we are trying to represent. (For example, if we are talking about different types of persons or organizations, let’s include the different categories of persons and organizations that are involved in our model of the world, as well as the relationships and constraints that hold among them.) Being formal refers to the ontology being machine-readable – that is, available in some language such as the Resource Description Framework Schema (RDFS) or the Web Ontology Language (OWL) that can be easily processed. And finally, and most importantly, shared reflects the notion that an ontology captures consensual knowledge; that is, it is not private to some individual, but accepted by a group.