It is imperative that e-Gov platform for the next generation achieves integrative administrative services via citizen's one-stop portal and back-office linkages among ministries and external organizations. This objective aims to make further advancement in system integration and coordination by employing cloud computing and service-oriented architecture (SOA). To achieve these goals, expertise knowledge must be provided as well-organized citizen services, for which e-Gov platform should be built upon loose-coupling of databases. Japan's e-Gov policy has addressed these needs and designed its national service platform using master registry for standardized metadata, which is the first attempt in the world. This paper discusses the objectives of Japan's e-Gov policy, the architecture of one-stop service platform, and its evolutionary process of back-office linkages using common registry. It is proposed to manage metadata in labor saving manners according to a matrix of operation and disclosure classes via pre/post-process filters assigned.