Metis defines a generic Controller class for managing instances of objects that provide shared system services to all AFEs on the workspace. The Controller class provides a graphical user interface for adding and removing system-service instances from the workspace and for allowing the user to select a specific instance to provide the service. Service-specific controllers extend the Controller class and implement service interfaces to provide the desired service. The services are explicitly configured using a GUI provided by the Controller. A user can also setup a specific instance of the service provider as a default for that service.
To access the system services, an AFE calls the getController() method. For example, should the AFE need access to the data store, it calls the getController() method, passing it the type of system service required, e.g., `DATASTORE'. The VEM returns the instance of the appropriate controller for that service. The AFE then uses the instance when it needs system services. The Controller in turn, delegates the request to the default service provider, or allows the user to select a service provider from the list of configured providers.
Metis also provides reference APIs for system services such as printing and data storage. The printer API allow an AFE to print, check the status or remove a print job. The data storage API allow an AFE to store and retrieve files from a data store.