datasets - old data

Question regarding datasets.

I've got a datasource set up where the definition is set to "query" and initially there is nothing in the datasource. Query similar to below :-

select NULL TASK_ID,
   NULL TASK_VERS,
   NULL AMEND_NO,
   NULL ISSUE_NO,
   NULL ISSUE_TEXT,
   NULL MI,
   NULL CAT_CODE,
   NULL DELETED,
   NULL DATECREATED,
   NULL DATEDELETED from DUAL where 1 = 2

The process is this, user generates an .xls file in another application and then uploads this to our FS app and we use api_datasource.importfromfile to import the .xls file into the datasource above. This works fine, our user then scrolls through the grid and selects a number of rows to import into our database. When the user closes the app the data in the "tmp" datasource is jsut discarded, next time he loads the app the datasource is obviously empty.

Now my question is this, behind the scenes in the formspider schema the datasource is linked to a real table that FS creates, in my case its called "DSI_62367", being a table I can select from it using "select * from DSI_62367" now when I do that I see all the previous data thats been loaded, when the app is closed this table does not appear to be cleared down?

One of our DBA's has queried this as some of the files the users load can be quite large (10k rows plus) and they can do this a number of times a day, he is concered regarding the space issues when the app goes live and the number of users increases.

Should this be being cleared down automatically, is there an api I can call to clear it down? We don't want to retain any data in this datasource.

Cheers Simon