The Resource-Event-Agent (REA) data model identifies these three categories of entities in business processes and establishes relationships among them based on the rules that underlay actual business practices. The model becomes more efficient when the principle of relational database design, i.e., normalization, is applied. However, the higher the level of normalization in the database, the higher will be the degree of information segregation. Therefore, to ensure the accuracy of the information retrieved, it is crucial to understand the database structure and apply queries with correct join operations. “Join” is one of the fundamental relational database query operations. Join handles the processes that determine how data from two tables will be merged and selected. In this paper, a taxonomy of the join operations applicable to the REA data model is presented: it classifies the combinations of the categorical components in the REA model, identifies the join operation, and links to AIS documents and reports