One of the most challenging objectives of mobile data management is the ubiquitous, any time, anywhere access. This objective is very difficult to meet due to several network and mobile device limitations. Optimistic data replication is a generally agreed upon approach to alleviating the difficulty of data access in the adverse mobile environment. However, the two currently most popular models, both Client/Server and Peer-to-Peer models, do not adequately meet the ubiquity objectives. In our views, mobile data management should adequately support access to any data source, from any mobile device. It should also eliminate user involvement by automating data selection, hoarding, and synchronization, regardless of the mobile device chosen by the user. In this paper, we present UbiData: an application-transparent, double-middleware architecture that addresses these challenges. UbiData supports access and update to data from heterogeneous sources (e.g. files belonging to different file systems). It provides for the automatic and device-independent selection, hoarding, and synchronization of data. We present the UbiData architecture and system component, and evaluate the effectiveness of UbiData's automatic data selection and hoarding mechanisms.