Indeed a standard ASCOM for DSLR'S ...
You use the USB/Serial connection to trigger shutter, and you use the PTP (picture transfer protocol) that most camera's support to retrieve the image, settings like iso need to be done on camera ...
That is how Ekos on Linux is able to interface with so many camera's, they use the GPhoto library, GP went further then the standard PTP protocol and can control many more things so you don't need the extra cable to control the shutter, you can even control iso and so ...
/Yves