Obligation change raises the ”frame problem” which is to characterise what obligations remain unchanged after an action has been performed. Many general solutions have been proposed but even if they are attractive from a thoretical point of view they have practical drawbacks. In this paper simple solutions are proposed thanks to the restriction to obligations that take the form of modal literals. These solutions are presented in the framework of dependence logic and of situation calculus, and it is shown that they are based on the same intuitive idea. This idea is to express that we have a complete representation of actions and circumstances that can change an obligation.