The description about the book "Patterns of Enterprise Application Architecture" at
http://www.martinfowler.com/books.html speaks about several major design issues:
The main topic areas are: how to layer an enterprise application, how to organize domain logic, how to tie that logic to a relational database, how to design a web based presentation, some important principles in distributed design, and handling of what we call "offline concurrency" - concurrency that spans transactions.
Regards,
Dan