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 defining content of the master program; creating a first derivative program of time-based media including one or more derivative elements defining content of the derivative program; defining first inheritance relationship between the master program and the derivative program, wherein the first inheritance relationship specifies at least one master element that is to be inherited by the derivative program; and causing the first derivative program to inherit the content of the specified at least one master element from the master program in accordance with the first inheritance relationship; creating a second derivative program of time-based media including one or more elements defining content of the second derivative program; defining a second inheritance relationship between the first derivative program and the second derivative program, wherein the second inheritance relationship specifies at least one element of the first derivative program inherited from the master program in accordance with the first inheritance relationship that is to be inherited by the second derivative program; causing the second derivative program to inherit the content of the specified element from the first derivative program in accordance with the second inheritance relationship; and after creating the first derivative program and the second derivative program: altering in the master program one or more of the master elements specified by the first inheritance relationship; propagating the altered one or more master elements from the master program to the first derivative program in accordance with the first inheritance relationship to create a revised version of the first derivative program in which the one or more elements previously inherited from the master program in accordance with the first inheritance relationship are replaced with the altered one or more master elements; propagating the altered one or more master elements from the first derivative program to the second derivative program to create a revised version of the second derivative program in which the one or more elements previously inherited from the first derivative program in accordance with the second inheritance relationship are replaced with the altered one or more master elements; and alerting a user to potential conflicts in at least one of the first derivative and the second derivative resulting from the propagation of the altered one or more master elements.