Social context information has been used with encouraging results in developing socially aware applications in different domains. However, users' social context information is distributed over the Web and managed by many different proprietary applications, which is a challenge for application developers as they must collect information from different sources and wade through a lot of irrelevant information to obtain the social context information of interest. On the other hand, it is extremely hard for information owners to control how their information should be exposed to different users and applications. Combining the social context information from the diverse sources, incorporating richer semantics and preserving information owners' privacy could greatly assist the developers and as well as the information owners. In this paper, we introduce a social context information management system (SCIMS). It includes the ability to acquire raw social data from multiple sources; an ontology-based model for classifying, inferring and storing social context information, in particular, social relationships and status; an ontology-based policy model and language for owners to control access to their information; a query interface for accessing and utilizing social context information. We evaluate the performance of SCIMS using real data from Facebook, LinkedIn, Twitter, and Google Calendar and demonstrate its applicability through a socially aware phone call application.