Those instructions are positioning control instructions.
The DABS instruction reads the absolute position (ABS) data when the Mitsubishi servo amplifier (equipped with the absolute position detection function) MR-H, MR-J2(S), or MR-J3 is connected. The data is converted into a pulse when being read.
The DDRVI instruction executes one-speed positioning by incremental drive. The movement distance from the present position can be specified with a positive or negative sign.
These are the basic explinations out of the Mitsubishi FX Programming manual. The FX Positioning manual explains these instructions in detail.