*2.2. Architecture*

The system is comprised of five main components: (1) an app on a mobile phone; (2) a commercial activity tracker; (3) a database with user (activity) data and persuasive messages; (4) a model-based reasoning engine to interpret the data and predict the effect of different coaching strategies; and (5) a communication engine that selects and sends questions and messages to the app. Figure 1 shows those main components.

**Figure 1.** Overall architecture of the Active2Gether system.

Figure 2 provides an overview of the most important data flows in the system. The details are provided in the following sections.

**Figure 2.** Overall data flow in the Active2Gether system.
