I often see the studies on the internet regarding dogs and what they are really trying to tell us, and I hate to say but I think so many are a complete load of rubbish. Recently scientists spent their time studying dogs every day and then analysed what they "said" to their owners. They got dog owners to record hours and hours of footage of their dogs, for the men in white coats to look through. This apparently would determine that dogs are in fact having deep and meaningful conversations with people.
Now, after weeks of studying, and a lot of money the results were in, and the scientists were delighted with their findings. It seems that a dog rolling over means scratch my tummy, however, it can also mean I'm hungry, the same as if a dog puts its head forward it means, I'm hungry or scratch me. Pressing their nose against something means, they want you to scratch them, or that they are hungry. Turning their heads means they may be hungry, or they want their head scratched.
Are you seeing a pattern here, basically every single thing your dog does means it is hungry or they want scratching. Now I am no big scientist but surely that could have been determined without spending loads, and wasting everyone's time. Everyone knows that dogs love two main things, food and attention.
Your dog is trying to tell you that all day every day, give them love and food and you have a winning combination for a friend for life. No scientists needed, just basic common sense and an understanding of how your dog thinks.