I apologize for being rather vague here, but I'm working on a project involving stock data and stock purchases. I'm sure I'm going to end up having to get a broker involved, but I was wondering if anyone knows of any documentation on the underlying technology involved with existing trading sites, as well as the channels through which systems like google finance get their information.
Note that I already know of the APIs from yahoo and tdameritrade that send out the data, I'm interested in the channels through which that data travels to them in the first place.