Association (cont.) ❒ When a collection must have a particular sequence, its values are indexed by position number ❍ Strings: $name = "Fred", $name[0] = 'F', $name[2] = 'e' ❒ When a collection doesn't have a particular sequence, its values are associated by keys ❍ Grocery List: Value for key 'Item 3' is the value 'Spam'