A graph def has nodes. Every node has
- Op: E.g. AddV2, Placeholder, Const.
- Name (namescope): This is also the name of the output tensor(s). To refer to a specific index, you can say "name:0".
- Inputs (optional): E.g. Const and Placeholder ops do not have any inputs.
Placeholder ops are fed from the user input? Const ops are fed from the variables folder?