The following use cases show how to use App-ID to control a specific set of web-based applications and how to use URL categories as match criteria in a policy. When working with App-ID, it is important to understand that each App-ID signature may have dependencies that are required to fully control an application. For example, with Facebook applications, the App‑ID facebook‑base is required to access the Facebook website and to control other Facebook applications. For example, to configure the firewall to control Facebook email, you would have to allow the App-IDs facebook-base and facebook-mail. As another example, if you search Applipedia (the App-ID database) for LinkedIn, you will see that in order to control LinkedIn mail, you need to apply the same action to both App-IDs: linkedin-base and linkedin-mail. To determine application dependencies for App-ID signatures, visit Applipedia, search for the given application, and then click the application for details.