Walter uses notifcation of events to drive its animation. The current version recognises object start, stop and state change, and message send and receive events.
Objects may generate explicit event notifications which are distributed to subscribers by the event manager. The current version of Walter can subscribe to notifications from Elvin or Project Pilgrim's PEN.
Other potential event sources are currently being investigated. These include OMG's COSS Event Service, change monitors for things like DCE's endpoint mappper and directory service, process monitors, Web server usage monitors, etc.
A paper describing an early version of Walter and the event manager Elvin was presented at the SDNE'94 workshop.