using remote code

Ignoring the issues of executing untrustworthy code can someone tell me why this won't work and how I can achieve this? Basically there is a remote php file on another web server that has a function in it. I want to execute this function in my own code... I'm guessing this probably won't work but it's a nice idea. The remote function accesses a database on the remote machine and returns an array of information. The more I think about what I'm trying to do the more stupid it seems.... Anyway any attempt to require or include the file works fine but then I can't use the function because it is "undefined". The php.net docs seem to imply that this is possible. Can anyone say if it is possible and if so what I am doing wrong please, ta.