In more than one way a REST API is similar to a restaurant. They both hide a very complex process of accomplishing a service (serving food or data) behind a nice, warm and welcoming presentation. And we need to bear in mind that presentation is the key: no matter what goes on behind the scene in the kitchen, the food and its presentation is the key. And your API is the menu, the door to the services provided by the server. Whatever goes on in the kitchen (your server's internal domain) is not the concern of your customers as long as the output and presentation is good.