Why HUE devices (e.g., HUE-Bulb, HUE bridge) are added as child devices? Who is/are the parent(s), and where can we get the source code of the parent(s)?

Hi, guys,
As said in the “How to connect Philips Hue devices” page, the SmartThings Hub will automatically detect and add the hue bridge and hue bulbs into SmartThings system.

So, after that, I guess there is a device handler associated with each hue device that runs either on the SmartThings Hub or in the SmartThings Cloud ( most likely in the SmartThings Cloud).

Then, I found the source codes of such device handlers, such as hue-bulb and hue-bridge.
Apparently, such devices are child devices of some other device or SmartAPP, since they are calling their parents using:
log.trace parent.on(this) in the hue-bulb
def result = parent.parse(this, description) in the hue-bridge.

Why the hue devices are added as child devices?
Who is/are their parent(s)?
Where can we get the source code of the parent(s)?

Thanks!