How to implement foreground message prompt via XML file

How to implement the foreground message prompt via XML file
Recently do a company project, need to implement a message prompt function, exactly is: when the user in the foreground through purchase or consumption, user information and amount of changes, in the bottom right corner of the site will appear a message prompt, detailed description of his actions
Another example: Users in the front desk after the withdrawal, the webmaster in the background after the reception, the front desk will pop-up prompt "withdrawal has been accepted", this pop-up non-Windows pop-up box, but very human, very good-looking, very light a prompt box, in the lower right corner of the show!
Look at the company to give an example, read the code after the implementation of the method is: the user in the foreground each purchase or consumption changes, in the database is also written to the XML file, and then the front desk will be prompted. What I don't understand is why the value of the XML file changes the foreground prompt to appear accordingly, this message prompt value, is how to read from the XML? How to trigger it automatically prompt out?


I am a newly graduated university student, just take part in the work, may be brain is more stupid, this question thought for a long time, still do not understand how to implement the message prompt through XML
I hope you seniors and fairy sister, can help enlighten, thank you!

------Solution--------------------
Perhaps the foreground uses Ajax, then set the timer, estimating the JS setinterval () function
------Solution--------------------
Users in the front desk every click Purchase, etc., will jump it?
If so, load the XML file when you load the new page. If you do not jump, then reload the XML file every time the AJAX submission purchase operation.
does not necessarily use setinterval (), the user can be triggered when the operation.
Actually read one of its JavaScript code to see the clues

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