distributed models

Hello, I am designing a web application that has several tiers including a Flex client, Rails server and SAP back-end. The application is an extension of functionality offered by SAP system. SOAP services are used communicate with the back-end. I am pondering on the implications of the fact that some of my data models are likely to be in the back-end and some in the Rails application and some are distributed (shared) between Rails and the back-end. I would appreciate any pointers toward relevant knowledge on this subject and if anyone tried something similar with Rails. Some of the questions I have to find answers to are: - How does one use ActiveRecord with shared models? - What are the implications of this type of distributed design? - Relevant design patterns.

thank you, Slava