I'm drawing a communication diagram for an application where you can buy books. I'm using domain-driven design and have a 'shop' object, a 'cart' object, and a 'book' object.
My first communication diagram, for when the user first comes to the site, is straightforward. I generate all HTML (to show all books and an empty cart) back end with the help of PHP. I use an MVC pattern; so first I send a message to a 'controller' which creates a 'shop' with 'book's and an empty 'cart' before sending these to the view.
(I have been searching for over five hours, but I didn't find anything on this topic. It's like it's not even an issue to people. Am I viewing this problem completely wrong? Otherwise any resources, or even search terms to use to learn about how to model (and code) these kind of things would be much appreciated)