Informally, the ontology of a certain domain is about its terminology (domain vocabulary), all essential concepts in the domain, their classification, their taxonomy, their relations (including all important hierarchies and constraints), and domain axioms.
Formally, to someone who wants to discuss topics in a domain D using a language L, an ontology provides a catalogue of the types of things assumed to exist in D; the types in the ontology are represented in terms of the concepts, relations, and predicates of L.
Both formally and informally, the ontology is the fundamental part of the knowledge, and all other knowledge should rely on it and refer to it.
Ontology is not active (cannot be run as a program).
An AI view: “Ontology is a specification of a conceptualization.”
- Conceptualization: an abstract, simplified view of the world, based on the concepts, objects, and other entities that are assumed to exist in an area of interest, and the relationships that exist among themFuzzy logic: a logic represented by the fuzzy expression, satisfying certain conditions
- Specification: a formal (machine-readable) and declarative representation
Ontology is a specific sort of knowledge base, characterizable as comprising a 4-tuple:
O = <C, R, I, A>, where
- C: a set of classes representing concepts we want to reason about in the given domain (vertices in a graph)
- R: a set of relationships connecting concepts (directed edges in a graph)
- I: a set of instances assigned to a particular concepts (data records assigned to concepts or relation)
- A: a set of axioms.
Ontology evolution process is sometimes identified as a six-phase evolution process:
Ontology evolution process
Various methods of ontology development are comparable in the following parameters: terms of use – development process – implementation process – preservation and use – knowledge obtaining – ontology control and confirmation – ontology configuration management – ontology documentation.
An example: The musical ontology
Literature
- Gašević D., Djurić, D., Devedžić V., Model Driven Architecture and Ontology Development. Springer-Verlag, 2006
- Ciza Thomas: Ontology in Information Science. ITExLi, 2018
- Davies J., Studer R., Warren P. (Eds.), Semantic Web Technologies: trends and research in ontology-based systems. John Wiley & Sons, Ltd., 2006