Informational Modeling and Relational Database

I am introducing Object Relation Modeling( ORM) as a process bfore UML based modeling can be used in Enterprise based modeling.

The reference that I am using is :

1.0 Information Modeling and Relational Databases- Using ORM with ER and UML- Terry Halpin- ISBN- 1-55860-672-6

In the first few chapters the information modeling seems an extention of semantic Modeling.
The author seems to suggest that we it is simpler to go from ORM based semantic modeling to Relational Entity- Relation Modeoing of Chen. I am not clear at this point hos this is done.
also since the ORm model gets big very quickly how do we control hierarchyy and multi page diagrams. More on this later.