...
v_sql_stat := 'SELECT * FROM '|| 
                    v_tab_own_upp || '.' || 
                    v_tab_name_upp || ' ' ||
                    v_my_where_str;
      
      /* "Activate" the generator. */
      v_ctx := dbms_xmlgen.newContext(v_sql_stat);
                                    
      /* Create the XML code. */
      v_xml := dbms_xmlgen.getXML(v_ctx);
      
      /* Closing the cursor. */
      dbms_sql.close_cursor(v_sql_stat_cur);
      
      /* Open the file for creating the xml. */
      v_xml_file := utl_file.fopen(par_path, par_file_name, 'A');
...

SQL> SELECT SYS_XMLGen
  2            (SYS_XMLGen(XMLAgg(XMLType('<'||column_name||'/>')))
  3              , XMLFormat.createformat('ROWSET')).getClobVal() data
  4  FROM   all_tab_cols
  5  WHERE  table_name = 'EMP' 
  6  ORDER BY column_id;

DATA
-----------------------------------------------------------------------
<?xml version="1.0"?>
<ROWSET>
<ROW>
  <DEPTNO/>
  <COMM/>
  <SAL/>
  <HIREDATE/>
  <MGR/>
  <JOB/>
  <ENAME/>
  <EMPNO/>
</ROW>
</ROWSET>