recommended way for server side validation - include in same file or have a different file

Hi I have always felt for reasons for cleanliness and clarity, it is better to have the validation and insert / update statements in a seperate file rather than have it in the same script. Case 1 ---------- //file:form.php if $_POST then validate Insert or update on success else if $_GET['primarykey'] then show form for editing else show form for adding fi <form action="form.php" method=post> Show form </form> Case 2 ---------- //file:form1.php if $_GET['primarykey'] then show form for editing else show form for adding fi <form action="formvalidate.php" method=post> Show form </form> However in the second case, in case of an error, displaying the data becomes an issue. Any recommended ways for server side validation -- Warm Regards ~~~~~~~~~~~~ Vinayak