What are Ontologies Useful For?

Background

The term ontology originates in Philosophy, where it is usually written with the capital initial letter and refers to the branch of this discipline that studies the basic categories of existing entities and their relationships.

In Computer Science, the term ontology does not usually refer to a global and unambiguous characterization of reality, but instead to the representation of a particular “viewpoint” about a portion of reality. This means that, in Computer Science, there can be many “ontologies,” often “partial” (i.e., referring to a part of the existence). For these reasons, the term is usually written without the capital initial letter and used in the plural. In Computer Science, ontologies are considered more interesting if they can be implemented by “computational objects,” exploitable in software applications.

Despite these considerations, Computer Scientists do not actually agree about the meaning of the term “ontology” and in the literature different definitions of the term “ontology” can be found. In Gruber (1993) it is defined as “an explicit specification of a conceptualization”; Borst narrows the definition by introducing the aspects of formal specification and sharing: an ontology is thus “a formal specification of a shared conceptualization” (Borst, 1997); in (Studer et al., 1998) the authors propose to merge these two definitions: “An ontology is a formal, explicit specification of a shared conceptualisation.” According to Guarino and Giaretta an ontology is “a logical theory which gives an explicit partial account of a conceptualization” (Guarino & Giaretta, 1995). This definition further narrows the meaning, by considering ontologies only logical theories and, in particular, stressing the fact that they are usually “partial” accounts of a conceptualization.

Since this last aspect is one of major importance, in this article we will (mainly) refer to the following definition of “ontology,” which integrates this concept within the previously mentioned definition provided by Studer and colleagues (Studer et al., 1998):

In the following, we will explain this notion of ontology by adopting a rigorous, but informal, approach. For a formal characterization, refer to (Guarino et al., 2009), among the others.

All the previously mentioned definitions mention the notion of conceptualization. A conceptualization is a set of elements, considered as existing in some portion of reality, together with a set of concepts and relationships which characterize (or enable to understand or to describe) that portion of reality, from a particular perspective. Notice that here we use the term “reality” in a broad sense (including physical entities, counterfactual ones, imaginary entities, and so on).