Client server

REST is about separating the client and server. This constraint is about "separation of concerns". It means that the server and client have separate responsibilities, so one is not responsible for the other's duties. For example, the client is not responsible for data storage on the server as it is the server's responsibility. In the same way, the server doesn't need to know about the user interface. So both the server and client perform their tasks and fulfill their own responsibilities which makes their work easier. Hence, the server can be more scalable and the user interface on the client can be independent and more interactive.