Explain the tables ResourceTypeHierarchy and ResourceAssociation, please.

I'm still in vacation mode, so take this with a grain of salt!

1) Resouce Association is straightforward in that you are simply associating one resource with another. Montior to Computer, Asset to Department, Update to Bulletin to Software that is vulnerable.

2) ResourceTypeHierarchy is a little more complicated, but my thought of it is, everthing has  base resource. For example Network Resource - Computer is a type hierarchy. For bulletins one example would be (top level first) All resources - software component - software update.

An additonal association could be made here with the software resource, and the command line.

 I think you've touched on one of the most complex part of the NS database.

Resource Hierarchy is complex to grasp from a db point of view because it uses tables to represent what can be only well described (for us human's) in the form of a tree.

And the same tables can be used to represent multiple points in the tree.

One good example of this is the ItemReference table that is used to build the NS console tree (with folders and nodes) all in a single table.

An additional problem with the ResourceHierarchy is that it maps to the Resource model, which is used to defined relationships between resources in a tree (again) and is implemented via Object Orientated programming (C#) in code via inheritance and composition (which are 2 of the pilars of OO with encapsulation and polymorphism).