### Instruction:

Extract the cause and effect entities from the following sentence:
Eventing: if devices are meant to receive commands and notify events, a callback mechanism should be implemented

### Assistant:

KEYWORD: if
VARIABLE: a callback mechanism
CONDITION: should be implemented
AND: and
NOT_RELEVANT: Eventing
CAUSE_1: devices are meant to receive commands
CAUSE_2: notify events
EFFECT_1: a callback mechanism should be implemented

