An overlay program is invoked by the service layer whenever a management application requests to retrieve or set the value of an attribute in the component. The overlay program is loaded into the service layer's process space and enables the service layer to directly access the attribute values through the overlay program's procedures. When the request is completed, the service layer unloads the overlay program.

Overlay programs are useful for components that do not already have resident code or for components running in systems with constrained memory. They are also appropriate if they are called infrequently. The data associated with your component is not retained by the overlay program between invocations, unless you specifically designate some storage mechanism for the values. If your component data must always be available, a direct-interface program is more appropriate.