The top layer of the architecture presents SNA Server Manager information to the user. This includes the SNA Server Manager user interface and automation controllers, such as a Visual Basic application. These components typically deal with configuration and management data, and receive notification of changes to the data either by polling or by implementing a special OLE object that is used to inform the application of changes to the underlying objects. The applications open a domain to initiate the reading of the configuration file and to obtain the status of data from all SNA Server computers in a subdomain.