1. In a computer-based system for multimedia composition, a method comprising: creating a master program of time-based media including one or more master elements; creating a derivative program of time-based media including one or more derivative elements; defining an inheritance relationship between the master program and the derivative program, wherein the inheritance relationship specifies at least one master element that is to be inherited by the derivative program; and causing the derivative program to inherit the specified at least one master element from the master program in accordance with the inheritance relationship.