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Definition
Ontology:
A representational artifact, comprising a taxonomy as proper part, whose representations are intended to designate some combination of universals, defined classes, and certain relations between them.1
Taxonomy:
A hierarchy consisting of terms denoting types (or universals or classes) linked by subtype relations.1
Hierarchy:
By “hierarchy” we mean a graph-theoretic structure consisting of nodes and edges with a single top-most node (the “root”) connected to all other nodes through unique branches (thus all nodes beneath the root have exactly one parent node).1
Types or universals:
By “types” or “universals” we mean the entities in the world referred to by the nodes in a hierarchy.1
Entity:
Anything that exists, including objects, processes, and qualities…. “Entity” thus comprehends also representations, models, images, beliefs, utterances, documents, observations, and so on.1
Ontology, terms, and representations:
Ontologies represent (or seek to represent) reality, and they do so in such a way that many different persons can understand the terms they contain and so learn about the entities in reality that these terms represent. Ontologies in the sense that is important to us here are designed to support the development, testing, and application of scientific theories, and so they will to a large degree be about the same sorts of entities as are represented by the general terms in scientific textbooks. Ontologies consist of terms arranged together in a certain way, and terms are an important subtype of representations.1
Representation:
An entity (for example, a term, an idea, an image, a label, a description, an essay) that refers to some other entity of entities…. Note that a representation may be vague or ambiguous, and it may rest on error.1
Artifacts:
Something that is deliberately designed (or, in certain borderline cases, selected) by human beings to address a particular purpose.1
Representational artifacts:
An artifact whose purpose is one of representation.1
Representational unit and composite representations
Representational units and composite representations are very common types of representations - encompassing practically the whole world of documents, which use written or printed language to represent things in the world. For example, the composite representation “John is drinking a glass of water,” asserted by someone who is watching John, picks out a process in the world. The representational units in this composite representation include “John” and “glass”; these are the smallest referring bits of language contained within the sentence (“J,” “w,” and so on do not refer to or represent anything). Other examples of representational units include icons, names, simple word forms, or the sorts of alphanumeric identifiers we might find in patient records or automobile parts catalogs.
- Representational unit: a representation no proper part of which is a representational unit.
- Composite representation: a representation built out of constituent sub-representations as its parts, in the way in which paragraphs are built out of sentences and sentences out of words.1