We present a three-tier architecture of middleware that addresses challenges facing accessibility, availability, and consistency of data in mobile environments. The architecture supports the automatic hoarding of data from multiple, heterogeneous sources into possibly a variety of different mobile devices. The middle tier enables the automation of synchronization tasks in both connected mode (following disconnection) and weakly connected mode, where only intelligent and effective synchronization can be used in the presence of a low-bandwidth network. We present the three-tier architecture based on the Coda file system. © 2001 IEEE.