Abstract-Data aggregation processes are essential constituents for data management in modern computer systems, such as decision support systems and Internet of Things (IoT) systems. Due to the heterogeneity and real-time constraints in such systems, designing appropriate data aggregation processes often demands considerable efforts. A study on the characteristics of data aggregation processes will provide a comprehensive view for the designers, and facilitate potential tool support to ease the design process. In this paper, we propose a taxonomy called DAGGTAX, which is a feature diagram that models the common and variable characteristics of data aggregation processes, especially focusing on the real-time aspect. The taxonomy can serve as the foundation of a design tool that enables designers to build an aggregation process by selecting and composing desired features, and to reason about the feasibility of the design. We also provide a set of design heuristics that could help designers to decide the appropriate mechanisms for achieving the selected features. Our industrial case study demonstrates that DAGGTAX not only strengthens the understanding, but also facilitates the model-driven design of data aggregation processes.