Design a ER Diagram that incorporates the specification described below as efficiently as possible:

A Yelp user has a unique yelp ID, first name, last name, gender, birthdate, birthplace, age, email, a profile picture, and list of friend ids. Yelp users can be complemented by their friends. A Yelp user can rate any business on a scale of 1-5 and provide reviews. A user has an " Activity Wall" where 10 most recent Yelp reviews by user's friends are posted on the wall when the user follows her friends activities. In addition, the user can checkin to a particular business.