search for: ecommerceactivity

I have problems on a simple design problem. I have many companies. Each company have one or more commercial activity. Activities types are: ecommerce, local unit, television, automatic vending machines, and so on. Company may have one or more ecommerce activity or one or more local unit activity, one ormore vending machines, etc. How can I model this scenario? Company has_many ecommerce has_many