In philosophy, ontology is the branch of metaphysics that deals with the nature of being. Although this can be taken to be the study of what it is for anything to exist at all, as in Heidegger's work, ontological questions are also concerned with what, in particular, exists. Thus our common-sense
ontology would include the material objects with which we interact (such as trees, tables, and mountains), but should it also contain abstract mathematical entities (sets and numbers) or the sub-atomic entities of the theoretical sciences (such as protons and muons)? Closely linked is the question of reductionism. For example, can minds be reduced to bodies, or mathematics to logic? A major question is how we are to decide ontological issues. Ockham's razor, the principle, formulated by William of Ockham in about 1340, that we should not multiply entities beyond necessity, is generally thought of as a principle in the theory of knowledge or epistemology, and was used as such by Russell. But in recent philosophy this has also often been linked to questions of meaning, as in logical positivism. Research Ontology
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Research Ontology