configuration - Adding Data.php Helper in Magento got error -

following alan storm tutorial in custom magento system configuration, when tried adding

the data.php in helper folder still error:

fatal error: class 'mage_helloworld_helper_data' not found in e:\xampp\htdocs\magento \app\mage.php on line 520

**alanstormdotcom\helloworld\helper\data.php** <?php class alanstormdotcom_helloworld_helper_data extends mage_core_helper_abstract { }   **alanstormdotcom\helloworld\etc\system.xml** <?xml version="1.0"?> <config>         <tabs>         <helloconfig translate="label" module="helloworld">                 <label>hello config</label>                 <sort_order>99999</sort_order>         </helloconfig>       </tabs>  </config>   **alanstormdotcom\helloworld\etc\config.xml** <?xml version="1.0"?> <config>         <modules>         <alanstormdotcom_helloworld>             <version>0.1.0</version>         </alanstormdotcom_helloworld>     </modules> <frontend>         <routers>             <helloworld>                 <use>standard</use>                 <args>                     <module>alanstormdotcom_helloworld</module>                     <frontname>helloworld</frontname>                 </args>             </helloworld>         </routers>     </frontend>     <global>       <helpers>          <class>alanstormdotcom_helloworld_helper</class>       </helpers>         </global> </config>  

i wanted learn.. know works in still me find why.. might miss

something.. thank you.

this bit wrong:

<global>   <helpers>      <class>alanstormdotcom_helloworld_helper</class>   </helpers>     </global> 

it should be:

<global>     <helpers>         <helloworld>             <class>alanstormdotcom_helloworld_helper</class>         </helloworld>     </helpers>     </global> 

_{(the <helloworld> tag corresponds module="helloworld" above)}