Abstract
We develop a constructional approach to ontology, focusing on sets, parts, and relations. On this conception of ontology, one starts with some constructors and an initial collection of objects. Then new objects emerge by construction, that is, from the application of constructors to objects. This approach, which is inspired by work of Kit Fine, provides a unified formalization of core components of prominent formal ontologies. Our project is also shaped by its intended application: the resulting theory is to serve as a top-level ontology for the Information Management Framework of the UK's National Digital Twin.