Might want to look into redis
. It's extremely fast (which is important for a chatbot) and very easy to use. It's just a key-value store, though, so if you're looking for layered logic like that example had with XML, this isn't your answer necessarily--but then again, you probably wouldn't want to store the logic in the database anyway.
Basically, look at Redis, but without more detail about exactly what you're doing, it's a little hard to help.