Child Key Options

Should a child inherit the identifier of its parent? Parent key and child sub-key are concatenated.

+ Key segments may seem more "natural".
+ Fewer joins are required for selects.
-  The key gets longer at each child level.

Should every table have its own serial key?

+ Every key is the same construction -
    very valuable for generic structures.
-  More joins are required to select.

Both work. Experiment in your model.