Hello Chandra, First thing the revision tables is:

po_headers_all, po_headers_archive_all, po_lines_archive_all, po_line_locations_archive_all and po_distributions_archive_all

Note: How the Purchasing Archive tables are updated when using Archive on Approve method for archiving (To setup Archive on Approve go to Setup -> Purchasing -> Document Types) and here an example to understand and to get the revision’s of PO 1- We created new PO, sent it for approval 2- PO Approved Now run this query :

SELECT po_header_id, segment1, revision_num 
FROM po_headers_all 
WHERE po_header_id = &p_po_header_id

which is (&p_po_header_id) is ID for po has been created above. and here is the result expected:

3- Now add a new line in PO, then sent it for reapproval. 4- PO Approved Now run this query

SELECT po_header_id, segment1, revision_num 
FROM po_headers_archive_all 
WHERE po_header_id = &p_po_header_id

So now from archive table you can get all revisions for particular PO.  

You can use the UTL_FILE package. For example, this will verify that you can create a new file named your_test_file_name.txt in the directory and write data to it

[code]
DECLARE
l_file utl_file.file_type;
BEGIN
l_file := utl_file.fopen (‘UR_DIR’, ‘some_new_file_name.txt’, ‘W’);
utl_file.put_line (l_file, ‘Content of the file’);
utl_file.fclose (l_file);
EXCEPTION
WHEN utl_file.invalid_path THEN
dbms_output.put_line (‘File location is invalid’);
END;
[/code]

Also you can use UTL_FILE.FGETATTR to check if your file is exist and readable or not for more info about UTL_FILE click here.

If you are looking for How to grant read and write on directory in oracle you can check my answer here

Regards.