A Doubt

hi, I have a question. Hoping someone may help me out. Can a PHP page say file "abcd.php" access a variable $xyz which is used in another file "mnop.php"? I mean can I refer to a variable whose value has been set in some other file. The point is that the file "mnop.php" after finishing its query and on a particular case loads "abcd.php". The reason is, I need to check everytime the file "abcd.php" is loaded, I should be able to determine that it was loaded by "mnop.php" and not by typing in the complete URL to "abcd.php" on the Web Browser. Hoping someone could tell me how if it is possible Best Regards, Manoj 'I have miles to go before I sleep, and promises to keep'