Thanks a million. That is simply genius. So, can I use any ERD tool that can export the design to XMI?

Actually I haven't used it yet, but I've seen they used it with UML diagrams from ArgoUML: https://www.odoo.com/slides/slide/xmi2odoo-from-an-uml-map-to-an-odoo-module-in-no-time-302/pdf_content

Strictly speaking, you will not need to manage E/R diagrams. You work with UML to model your classes then the ORM Odoo engine will create the database tables for you based on your model (you should not interact directly with the database).

Will it creat python class on .py and .xml views?

As I told you I haven't tried it yet, but I think it will just create the module classes (.py files) and not the views (XML). I'm still managing to understand the basic functions of Odoo and have a lot of problems with inheritance even with simple classes (there are a couple of questions of mine open here in the forum). I will test it as soon as possible. IMHO you create your UML models with classes using ArgoUML and then with xmi2odoo you will obtain the odoo modules (.py files) from your model that you can further personalize (anyway on github there is an example you can follow). Give it a try. It should work on version 8, I'm not sure you can use it with version 9 (you should verify it). Here is the example https://github.com/ingadhoc/xmi2odoo_example