Without the number being generated from a web service or a database, the
number isn't guarenteed to be unique.  You can probably come close, but it
won't be guarenteed.

If you aren't requring uniqueness, there are a number of ways to generate
almost random numbers.  However, there is no real way within the bounds of
the current form to create an incrementing number.  For that you would have
to, as you say, use a database or a web service.

--josh bertsch

Another way to have the number generated, but not sequential, is to use a
combination of date and time and employee ID. (Employee initials might be
duplicated)

If you need sequential, you don't have to use a database. You can accomplish
this with just a seperate XML form that only has the counter. Using code,
you can get the value and then increment it each time. This is a lot more
involved as you have to code retries if the file is locked.