A number of modeling approaches have been proposed in the literature for designing business information systems. This paper critiques prior data modeling approaches and presents an integrated object-oriented modeling approach that captures both the structural and the behavioral aspects of the business domain. Although there is considerable interest in object-oriented (OO) technologies in practice and in the information systems literature, there is no widely accepted OO modeling approach that facilitates the identification of objects from a business information processing perspective. Based on McCarthy’s (1982) resources, events, agents (REA) framework, the business process focused object-oriented ontology presented in this paper identifies the key resources, events, and agents in an enterprise information systems context. Termed OOREA, the ontology extends McCarthy’s REA model by capturing both the structural aspects of modeling, in terms of the objects of interest in the domain, and also the behavioral aspects in terms of the processes that modify objects. Application of the model is illustrated in the context of sales and related events for a retailing enterprise.