Also, when it comes to the Data Source, what does a company do to set something up on a machine so that it can send sets of data out to the interface node? Meaning, is there a device that connects to a machine, or how does that all work
Programmable Logic Controller, which was traditionally used for discrete control but in recent years it has taken on an expanded role with PID control, etc.
The interfaces connect to "something" - it's not a computer that's just send sending data, but an interface connects to a sensor, a control unit, another PI System, your SQL database, or even another file. Here are some videos talking about data collection: https://www.youtube.com/user/OSIsoftLearning/playlists?view=50&sort=dd&shelf_id=15
Let me know if you have questions.
Retrieving data ...