Holden,

Its difficult to determine a data format from the extension alone (but its a good start), however Clipper uses NTX index file(s) so this would be a good place to start.

The following is the physical structure of the NTX header so that you can check by loading the file into the hexeditor application that comes with VFP.

00h  unsigned signature - contains 09 if good NTX file
02h  unsigned version   - version of indexing system that the file was created 
                          under (0x1 is typical but may change)
04h  long root          - file offset (within the NTX file)where the root 
                          page is.
08h  long free_page     - file offset (withing the NTX file) where the first of
                          a list of free pages is. A 0 value ends the list.
                          The Clipper index system is intended to reuse free 
                          pages.
0Ch  unsigned item_size - the size of the item.
0Eh  unsigned key_size  - the size of the index key
10h  unsigned key_decim - number of decimal positions for the
                          key, if it is a numeric key.
12h  unsigned max_item  - maximum number of items per page.
14h  unsigned min_item  - minimun number of items per page (max_item / 2 
                          is typical)
16h  char key_expr[256] - an array containing the key expression for the index 
                          The expression must be terminated by null (ASCII 0) 
                          and its length cannot be greater than 256 bytes.
272h unsigned unique    - contains the value of the UNIQUE option for the index.
                          (1 = index is UNIQUE; 0 = Not UNIQUE)

The DAT extension is the default for DataFlex.

HTH
Neil