In NX 9, you can use the Product Interface command to specify geometry and expressions in your part that should be used as references.
A part file often has many geometric objects and expressions that can be referenced by other parts. You may find it convenient to limit the objects and expressions in your part that can be referenced by other parts.
In this video, Derek England talks about some of the new features in Product Interface.
You can publish the interfaces and their references to Teamcenter, which can track the usage of the interfaces by other parts.