System monitoring is a key function of a SCADA system and needs to be considered in terms of the necessary interaction between personnel and production processes.
You need to consider if the delivery of data is time-critical. For example, alarm conditions need to be presented in real time, trend data may be delivered with a slight delay, while maintenance data can be accumulated and viewed as necessary.
The system may also need to be monitored at different levels, from machinery operators to control room personnel managing plant-wide processes. For each level of monitoring, consider the data that needs to be presented, and the specific performance and diagnostic conditions that need to be flagged.