An information systems architecture is a specification of the information, computational elements, people, and underlying concepts in a services system. Accordingly, an associated data architecture is a specification of how data is stored, processed, and used in a system of record. A given data architecture effectively governs the flow of data in a system and establishes a relationship between an organization’s processes and it’s supporting information systems. Data architecture for an enterprise describes its applications, hardware, networks, business objects, business processes, and data. As such, it encompasses a complex set of definitions, methods, data types, and relationships. This paper introduces the concept of ontology applied to information systems and describes the essential elements of data architecture.