Ontology

Barry Smith's text “Ontology” was originally published as a chapter in the anthology The Blackwell Guide to the Philosophy of Computing and Information (ed. Luciano Floridi, 2003) — a broad collection with contributions from many different philosophers and researchers on a wide range of topics in the philosophy of computing. It's specifically Smith's chapter, not the anthology as a whole, that's relevant here: he provides a broad introduction to ontology both as a philosophical field and as a practical tool in information science, moving between philosophical ontology, methods for building ontologies, and how the concepts are applied in AI and information systems. The text is freely available as a preprint PDF, so you don't need to buy the whole anthology to read it.