The aim of this pattern is to ensure that a change in security is reported to each entity of the system that would like to be informed for a category of change. For example, a revocation of a certificate can be detected by an entity. She can, then, stop immediately a transaction established with the entity revoked.

Security can be very dynamic in grid environment. It is useful to provide variety of mechanism to detect and react to security changes. A mechanism like publisher-subscriber can manage these requirements.

This pattern can be applied when security changes must be detected to react immediately in order to take corrective measures.

The SecurityMonitor checks continuously some security properties. When a change occurs, he emits a corresponding event and notifies all observers about this event.

The SecurityObserver is an entity that wants to be notified when a change of security occurs in order to take correctives measures.

The Event is a piece of information concerning the change in the monitored security properties that have occurred.

When an observer need to be informed of changes of a security property, he subscribes to a security monitor in order to be kept informed and when a change occurs the subject notifies the set of observers that have subscribed.