The goal of implementing an enterprise digital engineering strategy is to improve data sharing throughout system conceptualization, development, manufacturing, operations, sustainment and their supporting organizations. Data sharing is a critical element of interoperability of models and other digital artifacts supporting the systems engineering process. Achieving interoperability within systems engineering requires eliminating differences of syntax and semantics to take advantage of automation, augmentation, and artificial intelligence capabilities that will increase process efficiency and artifact quality. This paper describes the development of a process-centric Systems Engineering (SE) reference ontology, based upon ISO/IEC/IEEE 15288 Systems and Software Engineering – Life Cycle Processes. The proposed SE reference ontology extends from the Basic Formal Ontology (BFO), which is a very small top-level ontology (TLO) designed specifically to support the integration of more specific ontologies that extend from it. A reference ontology is intended to provide a comprehensive representation of the entities in a given domain encapsulating the terminological content of established knowledge. Unlike other systems ontologies, which focus on the target systems, this reference ontology is focused on the systems engineering process, providing context and purpose for the digital artifacts being built and linking the content of artifacts together into one lexicon.