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<h1 class="sect1"><font face="arial, helvetica, sans-serif" color="#330099">About the Expression Framework</font></h1>
<p>The EclipseLink expression framework provides methods through the following classes:</p>
<ul>
<li>
<p>The <code>Expression</code> class provides most general functions, such as <code>toUpperCase</code>.</p>
</li>
<li>
<p>The <code>ExpressionMath</code> class supplies mathematical methods.</p>
</li>
</ul>
<p>This division of functionality enables EclipseLink expressions to provide similar mathematical functionality to the <code>java.lang.Math</code> class, but keeps both the <code>Expression</code> and <code>ExpressionMath</code> classes from becoming unnecessarily complex.</p>
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<h2 class="sect2"><font face="arial, helvetica, sans-serif" color="#330099">Comparing Expressions to SQL</font></h2>
<p>Expressions offer the following advantages over SQL when you access a database:</p>
<ul>
<li>
<p>Expressions are easier to maintain because the database is abstracted.</p>
</li>
<li>
<p>Changes to descriptors or database tables do not affect the querying structures in the application.</p>
</li>
<li>
<p>Expressions enhance readability by standardizing the <code>Query</code> interface so that it looks similar to traditional Java calling conventions.</p>
</li>
<li>
<p>Expressions allow read queries to transparently query between two classes that share a relationship. If these classes are stored in multiple tables in the database, EclipseLink automatically generates the appropriate join statements to return information from both tables.</p>
</li>
<li>
<p>Expressions simplify complex operations.</p>
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