Because these feature weights are dependent both on the input text and the output class, we sometimes make this dependence explicit and represent the features themselves as f (x, y): a function of both the input and the class. Using such a notation f 5 (x) above could be represented as three features f 5 (x, +), f 5 (x, −), and f 5 (x, 0), each of which has a single weight.