OneDbf:Ntx: read-only: array
  Index file definition in form of:
  Ntx:={}
  AAdd( Ntx, {cMenuName,cFileName,cKey,lUnique,lUserDefined} )
  ...
  Where:
  cMenuName    - menu item name, for enabling the selection of this index
                 file with SET ORDER TO
  cFileName    - is the index file name
  cKey         - is the key expression for this index file
  lUnique      - sets the index to be unique or no
  lUserDefined - sets the index to be user defined when runing the program
                 or no. (its flag is only for internal library use,
                 you can use it only in read-only mode)