https://doc.openerp.com/5.0/developer/1_3_oo_architecture/mvc/#mvc-model-in-openerp

In the Document says "From View to Model : the model sends notification to the view when its data has been modified in order the view to redraw its content."

1) Openerp how the model (The PostgreSQL tables) send notification to the view?.. In default openerp module database structure created with python file. How the model communicate with view?... can u please explain the openerp MVC examples with openerp module?..

2) what is the difference between Model-view-controller (MVC) is an architectural pattern and multitenant, three-tier architecture.