Most web applications of any complexity handle persistence to a greater or lesser extent. Shops must recall their products and their customer records. Games must remember their players and the state of play. Social networking sites must keep track of your 238 friends and your unaccountable liking for boy-bands of the ’80s and ’90s. Whatever the application, the chances are it’s keeping score behind the scenes. In this chapter, I look at some patterns that can help.