If it's in a Database then you'd have to have a datetime field of some sort that updates when the username the modified. When you run your statement, make the datetime field equal to "now()".
Well i am not storing the user names in a database, i want to know if there is a way using which we can retrieve the name of the user who modified the file the last time using information stored by the operating system
Oh. Well I'm pretty sure you can't get that. I don't think it is something that windows stores in the file natively. if you right click on the file and view it's properties that is all you'll have access to in the web page. You might have to look for another alternative. sorry.