The Yii Framework is very powerful and it provides a lot of functionality right from the pre-built webapp. One of the nice things that is already established for you as a developer is the Login authentication. While the default configuration simply sets it up to run against an array of hard coded usernames and passwords, the Yii Blog Tutorial provides a how to in connecting that login authentication method to a database so you can run your logins against the registered users. Talk about sweet deal.
A dropdown list can be used to select a value, based on which we can filter the data to be displayed. For example, the extension page has a dropdown list to filter the displayed extensions according to the selected category.