Once you have gathered the requirements, you do the domain analysis and identify the resources that need to be exposed. Be careful with the APIs that you make publicly available since, once they are presented, you cannot take them off without breaking clients. Remember, an API is a contract, and once it is offered, you cannot undo it without consequences. In our case, the consequences include breaking clients' apps and losing end users. That's why it often causes trouble when an API is a simple mapping to the internal data storage. You expose too much and create a tight couple between the clients and your internal implementation details. So, expose only what the clients actually need. No more, no less. Always start from simple and gradually evolve your APIs as you learn more about the consumers of your API.