To find an overview, definition, or summary of ontology and epistemology, it is likely that you will need to look outside of the standard healthcare databases. Instead, try using Reference or Humanities resources like these:
Use Advanced Search to look for "ontology" and then limit to the "Medicine" collection.
Repeat this process using the term "epistemology."
Look for "ontology" in the title, abstract, or assigned subject heading fields. Repeat this process with the term "epistemology."
Use Boolean Operators to combine your keyword terms.
Ontology, as a branch of philosophy, is the science of what is, of the kinds and structures of objects. In simple terms, ontology seeks the classification and explanation of entities. Ontology is about the object of inquiry, what you set to examine... the nature of being and existence.
From the University of Warwick
Epistemology is the theory of knowledge. It is concerned with the mind’s relation to reality. What is it for this relation to be one of knowledge? Do we know things? And if we do, how and when do we know things? Answering these questions requires considering the relationship between knowledge, truth, belief, reason, evidence and reliability. It requires considering the different psychological routes to knowledge, including different processes of reasoning – logical and scientific – introspection, perception, memory, testimony and intuition. And it requires considering the nature of the known reality.