How are OPC UA namespace used?

Question

I'm very new to the OPC UA and would appreciate your help with stuff that seems to be basic but I can't grasp it in full.

I'm exploring a publicly available OPC UA server at opc.tcp://opcuaserver.com:48010.

Here's the tree of nodes it exposes:

I'm trying to figure out what's the logic behind assigning namespaces here.

Path	Node Id	Comment
Objects	i=85	(I understand ns=0 is the default one and is omitted)
Objects/Demo	ns=2;s=Demo
Objects/BuildingAutomation	ns=3;s=BuildingAutomation	Why is it in a different namespace while it's under same parent?
Objects/BuildingAutomation/ControllerConfigurations	ns=3;s=ControllerConfigurations	BuildingAutomation is not part of the prefix?
Objects/BuildingAutomation/AirConditioner_1	ns=3;s=AirConditioner_1	Why doesn't it have BuildingAutomation in the prefix?
Objects/BuildingAutomation/AirConditioner_1/Temperature	ns=3;s=AirConditioner_1.Temperature	Why does it have AirConditioner_1 in the prefix?

Is it that we see multiple trees (each having its own namespace) merged here? Where do these trees come from? How namespace is assigned?

What's the logic behind node IDs without prefixes (ex. ControllerConfigurations ) vs with prefixes (ex. AirConditioner_1.Temperature) (as both seem to be attributes?)

Answer 1

Here is a great explanation.

Each namespace is a different model (tree of data):

Namespace 0 is defined by the OPC Foundation and contains OPC Core nodes that you cannot modify.

Namespace 1 is specific to your server can contains server info like certificates and open connections.

Namespace 2 ... n is where your business objects are.