How does darius conceptualize his empire and what are the expectations and obligations that he places on his subjects ?

Darius I (also called Darius the Great) saw his empire as a circle of territories all under his influence and rule. As he extended his conquests, he organized the Persian Empire into 20 satrapies (provinces), each of which could govern their own affairs to an extent, as long as they paid their proper tribute to the emperor.  He saw himself (and wanted to be seen) as the rightful ruler of all the lands from the Mediterranean to the Indus River. Subjects were obligated (in addition to paying tribute owed) to revere him with proper respect and obey any laws or decrees that he issued.

Absolute monarchy is that the monarch has the absolute or the supreme power verses constitutional monarchy which is that the head of state is elected and power of the monarch is limited. The main difference is the amount of power they each have.