Self-composition has another practical benefit—simplifying the design of privacy-preserving algorithms. Complicated mechanisms can be built modularly from simpler mechanisms in the same way software is built from functions. By controlling the information leakage of each component individually, a privacy-mechanism designer can control the information leakage of the entire system. In the case of ε-differential privacy, the privacy parameter ε of the final mechanism is at most the sum of the privacy parameters of its components.