So I had to duck out yesterday at 4, sorry, but I wanted to bring up a point that I think folks have been missing.

In information systems architecture work, we make a distinction between a functional architecture and a reference architecture. The functional architecture specifies what the functional units are, while the reference architecture specifies what the hardware and software units are. So taking the example Shuli gave of a refrigerator with batteries or Lorenzo gave of a solar farm with storage, these are entities in the reference architecture. In the functional architecture, they would consist of two functional units, one for load and one for source. A normal fridge would only have a single function, for load.

Typically, the control APIs (more recently) or protocols (historically) tend to follow the functional architecture, so a single reference architectural entity might have several functional APIs.

            jak

Hope that helps.