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<h2 class="first-section-title"><a name="202"></a><a name="ch06lev1sec4"></a>Identifying Attributes</h2><p class="first-para">Attributes are fields that a class contains. At a code level, attributes are instance-level variable declarations. Most attribution occurs with VOs, with other object types receiving little attribution.</p>
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<p class="para">Ideally, attributes should be base, not derived. A <b class="bold">base attribute</b> is atomic—that is, its value is not derived from the value of other elements or the result of a calculation. Conversely, a <b class="bold">derived attribute</b> is made up of the values of other elements. For example, consider a <span class="fixed">CustomerVO</span> class that has <span class="fixed">firstName</span>, <span class="fixed">lastName</span>, and <span class="fixed">fullName</span> attributes. The attribute <span class="fixed">fullName</span> is derived because it is made up of the first and last names.</p>
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<b class="bold">Avoid declaring derived attributes.</b> Derived attributes, like <span class="fixed">fullName</span> mentioned in the previous paragraph, only give you more to maintain. If a customer changes his or her last name, the values of two attributes need to change. Instead of making <span class="fixed">fullName</span> an attribute, it would be better to create a method, such as <span class="fixed">getFullName()</span>, that does the concatenation.</p>
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