Node Definitions

[Paul J DeCoursey]

Is there a way to define Node Types in a Implementation independent 
manner?  This is my first look at Content Repositories so forgive me if 
this question is naive.  I'm building a content management system and I 
need to make it completely independent of Jackrabbit so that our 
customers can just plug in whatever system they want.  For example once 
IBM gets Content Manager JSR-170 ready. Does this make sense?  Or is it 
that all systems will have their own way of defining node types and it 
just cannot be done through JCR?

Thanks