Ontology is the study of being or reality. It deals with questions about what entities exist and how they can be grouped, related within a hierarchy, and subdivided according to similarities and differences. There are differing philosophical views about the nature of reality, including whether reality is objective and exists independently of human observation, or is subjective and constructed through human experiences and social interactions. Ontological questions also concern whether social entities should be viewed as objective, external realities or as social constructions.