In this section we will cover the different programming models that emerged to address the near real-time updating of the client view based on the updates that are produced by the server.
As mentioned before, HTTP, which is the foundation of communication over the Internet, uses a simple request/response model in which a request either timeouts or get a response back from the server. The response can be the actual response the request was intended for or it can be an error message, underneath one of the standard error status codes. The client always initiates the communication; the server cannot initiate a communication channel without receiving a request from a client to send back a response.
So, basically, to update the client it is required to check for the new updates on the server and if an update is available the client can react to the update and, for example, change a text to denote that a book that was not available is available for borrowing now or a...