The thin-client programming model described in the previous section recommends a general software architecture that allows applications to be written flexibly and to run within a manageable and fault-tolerant environment. However, to build these applications from scratch would be very difficult. The Metis framework, shown in Figure 2, presents Java classes and interfaces needed to make programming these applications easier.
The Metis framework provides instances of the key objects discussed in the programming model including the workspace, user profile, AFE loader/launcher, VEM, directory client, service-stub loader, and controller objects. It also manages AFE objects. In addition, interfaces are provided to assist the application developer with the task of writing a thin-client application. These interfaces can be grouped as follows:
The following subsections discuss the interfaces shown in Figure 2.
Figure 2: The figure shows important classes in Metis and their relationships.
AFEs acquire a handle to the Workspace by implementing the AFEInterface.
Workspace implements the VEMInterface and the ControllerInterface,
and thus provides the necessary support for AFEs. Workspace uses
delegation (to the VEM object) in implementing the VEMInterface.
The workspace object contains VEM, controller, and UserProfile objects,
and manages AFE instances.
