In reply to mitesh.patel:
The mirrored value is the current state of DUT and desired value is the testbench part which contains value which testbench wants DUT to have by programming. (Similar to a monitor and driver respectively)
Mirrored value can get changed at run time inside DUT. Desired value is the value programmed or predicted by testbench.
Example: Writing “enable” to some register to enable some functionality changes the desired value. Checking the “status” bit of some register corresponds to checking the current status of DUT that can be checked by mirrored value which is last known state of DUT
Please refer code examples of RAL for further details