In the first phase of implementation, the SSIs serve as a simple interface layer between the CI and the user at each subsystem. They receive messages from the CI and display them to the user who takes any necessary actions. They also report any changes to the CI, and this is done by sending a message to the CI with the changes.
In the next implementation phase, some of the actions will be automated and the user at each subsystem will be notified with any action taken. For example, updating a data file that is used by the subsystem can be automatically done by the SSI, given that it has the necessary information about the file format and the location of the changed data.