PHP How can I fix this error? Fatal error: Cannot redeclare class iSerializable
<p>I am having a problem with detecting if an interface class is already declared</p>

<p><em>Error reported is:</em></p>

<p><strong>Fatal error: Cannot redeclare class iSerializable in /public_html/application/AppCode/iSerializable.interface.php on line 3</strong></p>

<pre><code>line1: //nothing here
line2:  require_once($filename);    
line3:  interface iSerializable
        {
            public function writeXML(DomDocument $doc, DomElement $element);
        }
</code></pre>

<p><strong>If this was a normal class, then i would have used this example function given below</strong> </p>

<pre><code>if(class_exists('iSerializable') != true)
{
   //put class iSerializable here
}
</code></pre>

<p><strong>but here, this class is an Interface, how can i check if this interface is already declared?</strong> </p>

<p>Can any one kindly suggest me a proper way or solution to this problem?</p>
