input: [Category] Operations [Description] The classic use for callbacks in WCF is for events. The service can maintain a list of callbacks, and notify them when some event takes place on the service side. The service contract can define subscribe and unsubscribe operations, and take a masked enum to allow the clients to chose which event to subscribe or unsubscribe to. In fact, you can even use delegates on the service side to manage the subscribers. This use in an interesting bridging concept: the service uses conventional delegates to manage and publish events, when the events are delivered using WCF duplex callbacks. [Last Updated] 9/7/2006 [Title] 
output: Events