
a transaction finishes, the changes are not lost. Together, the
properties of <span class="emphasis"><em>atomicity</em></span>, <span class="emphasis"><em>consistency</em></span>,
<span class="emphasis"><em>isolation</em></span>, and <span class="emphasis"><em>durability</em></span> are known as the ACID
properties.</p>
        <p>As is the case for concurrency, support for transactions varies among
databases. Some offer atomicity without making guarantees about
durability.  Some ignore isolatability, espe