Mobile devices have become general-purpose computers that are equipped with sensors, constantly access the internet, and almost always accompany the user. Consequently, devices manage many different kinds of data about the user's life and context. There is considerable overlap in this data, as different applications handle similar data domains. Applications often keep this data in separated data silos. Web applications, which manage large amounts of personal data, hardly share this data with other applications at all. This lack of interoperability creates redundancy and impacts usability of mobile devices. We present a data management architecture for mobile devices to support interoperability between applications, devices and web applications at the data management level. We propose a central on-device repository for applications to share resource and context data in an integrated, extensible data model which uses semantic web technologies and supports location data. A web browser interface shares data with web applications, as controlled by a general security model.