It's almost like an emotional state. What is complex for dogs is smell, the way they read the local bulletins pissted by all the locals, their health, their fertility, what they have been eating, their emotional state. And then they can leave their own peemail for others to smell and get all the latest community news :)
I don't know if they are necessarily intended to provoke. Some are definitely intended to warn and I think greet sometimes as well based on my own dogs' barks.
I'd say that depends on the warning bark and my dogs have more than one kind. There are kinds they seem to do to sound fierce and there are kinds they seem to do in order to get my attention.
But the greeting bark is definitely not provocative, it's just "open the door now now now now now pet me!"