what is the name of the convention used in this syntax diagram

I found this diagram in the JSON specification:

_{(source: json.org)}

Where does this diagramming convention come from? Is it just some random convention cooked开发者_JAVA百科 up by D.C.?

That's called a railroad diagram. Have a look at the wikipedia article for more information.

That diagram is known as a syntax diagram or railroad diagram. It's used to visually represent context-free grammars. It's a graphical depiction of the Extended Backus-Naur Form, which is also used to represent context-free grammars.