A system’s functionality is often realized by interaction of many independent products. The interoperability can cause problems in management and design, because these products possess different life cycle durations. Improved interface definition can facilitate the interaction of products within the system even if products possess such differences in their life cycles. In this paper a matrix and graph based approach is presented, which enables developers to ensure robust interoperability of products during a system’s life cycle. Relevant interfaces between interacting products are selected for more detailed consideration by systematically identifying critical and fast changing interfaces. This helps defining future-proof interfaces. The approach has been successfully applied in an industrial design project on safety relevant system development.