I. INTRODUCTION
Smart mobile devices have been the pivot for personal services. A large number of diverse sensors around the mobile device will enable highly proactive services with the help of a lot of personal context-aware applications, e.g., dietary monitoring [1], daily life assistant [5], sports training, interactive art [2], chronic disease monitoring, and elderly support, and health monitoring [3] [4], pervasive gaming [30] [31]. Situational appropriation of such services without user intervention requires an involved process for acquiring individuals' contexts. Individual users have different service requirements and preferences such as the system's level of proactive-ness and users’ privacy concerns. Applications require different types of contexts in different degrees of awareness. Future services will require much broader coverage and higher accuracy in recognized contexts.