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<h1>XSD Attributes</h1>
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<p class="intro">All attributes are declared as simple types.</p>
<hr />
<h2>What is an Attribute?</h2>
<p>Simple elements cannot have attributes. If an element has attributes, it
is considered to be of a complex type. But the attribute itself is always declared
as a simple type.</p>
<hr />
<h2>How to Define an Attribute?</h2>
<p>The syntax for defining an
attribute is:</p>
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<td>
<pre><xs:attribute name="xxx" type="yyy"/></pre>
</td>
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<br />
where xxx is the name of the attribute and yyy specifies the data type of the
attribute.<p>XML Schema has a lot of built-in data types. The most
common types are:</p>
<ul>
<li>xs:string</li>
<li>xs:decimal</li>
<li>xs:integer</li>
<li>xs:boolean</li>
<li>xs:date</li>
<li>xs:time</li>
</ul>
<h3>Example</h3>
<p>Here is an XML element with an attribute:</p>
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<td>
<pre><lastname lang="EN">Smith</lastname></pre>
</td>
</tr>
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<p>And here is the corresponding attribute definition:</p>
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<tr>
<td>
<pre><xs:attribute name="lang" type="xs:string"/></pre>
</td>
</tr>
</table>
<hr />
<h2>Default and Fixed Values for Attributes</h2>
<p>Attributes may have a default value OR a fixed value specified.</p>
<p>A default value is automatically assigned to the attribute when no other
value is specified.</p>
<p>In the following example the default value is "EN":</p>
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<td>
<pre><xs:attribute name="lang" type="xs:string" default="EN"/></pre>
</td>
</tr>
</table>
<p><span class="834132720-09042002"><strong style="font-weight: 400">A fixed
value is also automatically assigned to the attribute, and you cannot specify another value</strong></span>.</p>
<p>In the following example the fixed value is "EN":</p>
<table width="100%" border="1" class="ex" cellspacing="0">
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<td>
<pre><xs:attribute name="lang" type="xs:string" fixed="EN"/></pre>
</td>
</tr>
</table>
<br />
<hr />
<h2>Optional and Required Attributes</h2>
<p>Attributes are optional by default. To specify that the
attribute is required, use the "use" attribute:</p>
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<tr>
<td>
<pre><xs:attribute name="lang" type="xs:string" use="required"/></pre>
</td>
</tr>
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<br />
<hr />
<h2>Restrictions on Content</h2>
<p>When an XML element or attribute has a data type defined, it puts restrictions
on the
element's or attribute's content.</p>
<p>If an XML element is of type "xs:date" and contains a string like "Hello
World", the element will not validate.</p>
<p>With XML Schemas, you can also add your own restrictions to your XML
elements and attributes. These restrictions are called facets. You can read more about
facets in the next chapter.</p>
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