g about relational database theory requires that the system
support transactions, but most commercial relational systems do.</p>
        <p>Concurrency means that multiple users can operate on the database at
the same time. Support for concurrency ranges from none (single-user
access only) to complete (many readers and writers working
simultaneously).</p>
        <p>Transactions permit users to make multiple changes appear at once.  For
example, a transfer of funds between bank accounts needs to be a
transa