Product line engineering (PLE) is one of the recent and effective reuse approaches, and it consists of two processes; framework engineering and application engineering. Framework engineering is to model and realize a core asset which represents common functionality and quality attributes in a target domain, and application engineering is to generate a target product by instantiating the core asset. Hence, a core asset is a key element of PLE, and the quality of core assets largely determines the overall quality of products. Although numerous PLE methodologies have been introduced, it is still unclear what should be the elements of a core asset and how the core asset should be instantiated for each application. That is, the overall process and instructions of instantiating core assets have not been studied enough. In this paper, we first define a meta-model of core assets, propose a process of instantiation, and define its instructions on how to carry out each activity in practice. We ...