
The figure above describes how the user messages work. As you can understand, in order to send a specific message to a user of the system, a login is required. When the user logs in, the system takes his/her account information and compares them with the ones in the data base. When a user is authenticated, he/she is able to send a message to any user of the system. User details are kept when a message is sent, in order to see from whom the message came.

In the figure above you can see s deployment diagram of the system execution. The user sends a specific request from the web application to the server via HTTP protocol. There the request is analyzed and sent to the my SQL database if needed. When a process is finished with the execution, it comes backs to the user and it shown to him as an interface from the web browser.