I have been learning a bit about building management systems (BMS) and realized that, abstracted the right way, the manufacturing execution systems (MES) of semiconductor fabs are pretty similar in overall concept and components. That parallel made it much easier for me to frame my learning.
The brains of the system: BMS vs MES.
These s/w systems take schedules, control targets and feedback to make the building "work" (literally).
Granted, building equipment use many more protocols than just BACnet, some of which are proprietary to the equipment vendor.
The building equipment which is actually being controlled for the purpose of making the building useful for its owners.
An office building could be thought of a making an environment conducive to worker productivity with maximum efficiency.
A fab could be thought of as controlling the flow of materials between equipment to maximize output of wafers/chips at minimum cost.
The sensor systems which allow the control system to make smart choices about controlling the building equipment.
For an office building this might mean feedback control for HVAC (don't over cool) and switching off unused lights or dimming lights for daylight harvesting.
For a fab this might mean monitoring the voltage and flow rates for a particular piece of process equipment and adjusting the process recipe for the next lot or wafer to ensure uniform film properties from lot to lot.