SIC consists of many different objects. You can read about each of them on their respective pages. This is the inheritance hierarchy:
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Component
Sensor
Service
Actuator
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ComponentManager
...
Connector
...
Device
...
SICRedis
Message
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Request
StartComponentRequest
CompressedImageRequest
TextRequest
ControlRequest
ConnectRequest
PingRequest
StopRequest
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NotStartedMessage
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ConfMessage
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AudioMessage
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TextMessage
...
CompressedImageMessage
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UncompressedImageMessage
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BoundingBoxesMessage
ControlMessage
...
PongMessage
...
SuccessMessage
...
Sensors provide streams of data to their respective output channels. Other SIC components can then subscribe to these channels and use the sensor data.