Sybase SQL Anywhere/Ultralite
The current mobile database market leader (with over 60% market share) is the SQL Anywhere product from Sybase. The original version of this product was targeted at mobile laptop users who needed to sync up with server versions of the Sybase database (now named Adaptive Server Enterprise). Over the years, the product has grown to include a scaled-down relational database, known as Ultralite, that can be deployed across a variety of platforms and that supports a number of synchronization options. While the SQL Anywhere database is a powerful SQL database complete with security and high-end database functionality such as stored procedures and triggers, Ultralite will be of most interest if you're deploying applications to multiple mobile platforms. Currently, Ultralite is available for Windows 95/98/NT, Palm OS, Windows CE, and EPOC. APIs are available for C/C++ and Java, and these APIs remain the same across all supported platforms.
Unlike other relational database systems that have been ported to mobile devices, the Ultralite database was designed specifically for devices with no hard disks. This means that the database has been optimized for in-memory usage to provide high performance with minimal memory usage. The other powerful capability included with SQL Anywhere is the MobiLink synchronization technology. MobiLink is a server-based synchronization engine that can communicate with remote clients via a serial, TCP/IP, HTTP, HotSync, ScoutSync, or ActiveSync connection. Use of a common synchronization technology such as MobiLink can drastically cut the cost of development, as MobiLink handles advanced syncing operations such as snapshot and time-stamp synchronization, primary-key maintenance, conflict detection and resolution, and differencing. On the server side, all MobiLink synchronization logic is handled through the development of events using the SQL "flavor" of your back-end database. (MobiLink connects to the database via ODBC, so virtually all SQL databases are supported.) Public-key encryption is supported through the use of Certicom's SSL/TLS Plus (using elliptic-curve encryption technology). All things considered, the SQL Anywhere/Ultralite combination is an extremely powerful mobile database and synchronization solution that can handle virtually any task.