This document has been essentially written by Oracle Consultants familiar with both the 11.5.X and R12 architectural and functional differences.
This document is intended for IT application teams within end user accounts who might be considering and who might be participating in an upgrade from 11.5.X to R12. It provides some insight into the architecture and the functional differences that need to be considered when planning and scoping and staffing such an effort. And so in that regard, this more of a technical document.
Oracle apps 11.5.x to r12 functional and architectural differences 2011-02-24
Oracle apps 11.5.x to r12 functional and architectural differences