DOORS NG 6.0.3 - Fine-grained components - relations/hierarchy?

Components in DOORS NG and RQM  provide a scope for streams and baselines (aka configurations).
Within a component you can branch to create another stream, and you can deliver change sets in DOORS NG to multiple streams.
Within DOORS NG and RQM components have no hierarchy.

Within the Global Configuration Management (GCM) app, you define components, which provide scope for Global Configs (GCs).
Global configurations (GCs) include contributions of streams and baselines from other tools, or other GCs.
You express hierarchy among configurations by making one GC a contribution to another GCs.

A GC can contain other GCs. That's how you build hierarchy.

You can learn more here:

1.Jazz.net library: Welcome to configuration management in CLM version 6 releases