The study of existence; the study of being (something rather than nothing) and the ultimate nature of things; the study of a broad range of categories of existence, which also asks questions about the existence of particular kinds of objects; an ontology allows for (or provides) a more detailed specification of the relationships in a domain (or kingdom) – more explicit in mapping the relationships than a thesaurus, glossary, or taxonomy. A branch of philosophy (focused on knowing what exists), contrasted with epistemology (knowing how you know).