There's plenty of methods. The one I use is just linear algebra; it's basically just counting. I prefer not to use graphs unless I'm trying to find patterns in sound. Some major companies prefer that you have experience using praat for that task, it's openware so try it out if you're working with sound. I like to go straight to the source though and use bits as opposed to graphs because it seems to be a lot easier to work with (and MUCH more precise. It's basically 100% confidence with identification), but if you're using python, you can import graph modules. Making probabilities, or using statistical inference, is mostly useful for determining the boundaries between units of knowledge so you don't accidentally interpret more than what's usual. Beyond that, it's just making the program pretty (like by adding confidence thresholds). If you have any specific questions I'll help. It's amazing what people are able to do with machines now that we've discovered pattern recognition.
http://youtu.be/pp89tTDxXuI
I think I said this in a different thread, but most of what I've been seeing from the intellectual community are toys. I know that google and amazon have ambitions but from the google frontier, I really haven't seen any advances for some time. Last one I noticed was about 3 years ago with speech recognition. They do have quick answer boxes too but it's not anything like AI at this point. The FBI is using facial recognition now, so that's good news, but the potential for this type of software is huge. You just need to be able to sell yourself.