Some theory on diagrams:
I thought of a diagram as a couple of different things that are actually the same thing. First, I would describe a diagram as a picture showing an object in parts. This would usually be informational meaning it would have each part of the object broken down and described in some detail on the function of the part. Diagrams could also be used to show how to operate or assemble something in a similar way that it describes parts.
The diagram has a very vital role in architecture. The reading I did described it as an agency. To me this made it seem like a group of people with a few jobs that permeated each other. The first was the author, second was the object, and the third was the receiving subject. More importantly, it focuses this relationship. Without the diagram, we could still have the building, and we would know that someone had to have created it and lastly, someone would be viewing it and receiving whatever history the object presents. But the diagram is what fuses all of this together in one place, making it possible to make the connection between author, subject, and consumer.