In practical calculations, the theory presented above can be applied in two different ways, either as a subsystem method for treating a large system efficiently (i.e., the target is the full system and all subsystems are treated on an equal footing) or as an embedding method (i.e., the target is one specific subsystem, which is embedded in an environment composed of all other subsystems). The former case is typically known as Subsystem-DFT (sDFT).