In this paper we analyze the process of mapping business policies into object-oriented software structures. We stress that separation of concerns is a key strategy for obtaining high quality and evolvable implementations. In particular, we show that a naive mapping of business policies into object rules may result in a bad design compromising the overall software stability. We first present our work in the context of customizable of e-commerce applications, and briefly explain why customization functionality should be dealt by separating concerns. We next present our approach for combining object rules with other object-oriented design structures; we show that these modular software constructs allow seamless evolution and maintenance.