@aptiko Really Thank you for your sincere answer! I've been a web developer since 2000 and I always made database procedure on oracle, sqlserver and mysql to make billing, accounting and SCM, CMS like system. They all have complex and many database tables(about 100~200) and thier relation is so complicated and also have many rows(over billian rows). Can ORM handle complicated and big data within reasonable response time? And I also wonder how can I change database schema in live environment? Could you recommend articles or books which explain about more live environment.