Blackboard Parenting is a feature in NodeCanvas that allows you to assign a parent Blackboard to another Blackboard and thus in essence “inherit” variables from that parent Blackboard. More specifically this can be done in the inspector of the Blackboard component, within which an Asset Blackboard can optionally be assigned in the “Parent Asset Blackboard” field.
An Asset Blackboard is another type of Blackboard that you can create in your project through the “Create/ParadoxNotion/CanvasCore/Asset Blackboard” right-click menu in any assets folder. In contrary to a normal Blackboard, this is of course an Asset rather than a Component and thus can have no scene object references. Once a Parent Asset Blackboard is assigned to a Blackboard, all of its variables will show within the child Blackboard inspector as well, hence separated.
Within any of the graphs that use the child Blackboard, all parent Asset Blackboard variables will also be possible to be selected in all variables selection dropdowns as normal, as if the parent blackboard variables were part of the child blackboard. Naturally, this is very powerful because you can use the same Asset Blackboard as parent to any number of children Blackboards and thus create a “network” of variables that best suit the project use case by separating the gameobject variables from application variables as well as sharing some common variables between multiple gameobjects and agents.