A moern notification system is a combination of software and hardware that provides a means of delivering a message to a set of recipients. For example, notification systems can send an e-mail when a new topic has been added to Wikipedia. The complexity of the notification system is often dependent on the types of messages that must be sent. An e-mail noting when a page has been inserted into Wikipedia is adequate for such a straightforward task. However, notifying individuals when a building is on fire would require real-time interaction, escalation, scheduling, rosters, and fail-over scenarios.