Understanding API

API stands for application programming interface; it is an interface for the website (or mobile application) to communicate with the backend logic. Simply put, it is like a messenger that takes a request from the users and sends the request to the backend system. Once the backend system responds, it will then pass that response to the users. A metaphor for this is a waiter/waitress, who can understand different customers' orders. They will then act as a middleman between the customers and the chefs in the kitchen.

If you were the boss of the restaurant, the key benefit of having a waiter/waitress here between your customer and the kitchen is that the customers will be shielded from seeing your business secrets. They don't need to know how the meal is prepared. They just need to send an order through the waiter/waitress, and they will get the meal they ordered. In this scenario, the waiter acts like the API. The following figure helps illustrate the analogy.

Figure 1.1: The waiter acting as the API for the customer

Similarly, in computer science, one of the key benefits of having API is encapsulation. We encapsulate the logic so that people outside won't be able to see it. With this arrangement, big companies with sensitive information are willing to provide services to the world through APIs, confident that their internal information won't be revealed. Take Skyscanner again as an example. The company is comfortable with using an API to allow customers to book their flights, but at the same time, personal data from other customers that are stored in their internal database won't leak.

An API is also a standard interface that can communicate with different types of frontend Terminals, they can be mobile applications or websites. As long as the frontend is sending the same request to the API, it will get the same result back. If we go back to our metaphor, the waiter/waitress will serve all kinds of customers, regardless of their gender, age, language, and so on.

Now, imagine you are a software engineer at Skyscanner who is responsible for developing an API. What will your job be? Let me tell you. Your job will be to write a program that can take booking requests (date and location) from customers through the website, and then look up matching flights in the Skyscanner database and return the flight details to the customers. Throughout this book, you will be our API engineering intern. We will guide you, step by step, through the process of developing a RESTful API project that can serve the users of your system.