Every application deployed to App Engine is identified by a unique application ID and version. The version lets you distinguish between releases of a particular application, all of which can reside on App Engine simultaneously. You can obtain new application IDs and manage the different versions of your application via the App Engine Administration Console.
The application ID and version for a particular App Engine project are defined by
appengine-web.xml file, found in the
The application ID can be specified when you first create your web application and choose to use the App Engine SDK
in the New Web Application Project wizard.
You can view and edit the application ID and version after creating your application by right-clicking the project and
selecting Google > App Engine Settings....
Click on the My applications... link to view the applications you've already created on App Engine. To see the existing versions of your application, enter its application ID in the Application ID field and click the Existing versions... link.