Web Services Specifications on Eventing and Coordination

The WS-Events specification consists of ‘a set of processing rules for advertising, subscribing, producing and consuming Web services Events’. All authors of this specification are based at Hewlett-Packard. Further development of WS-Events is not on the agenda anymore. Therefore we only give a brief overview of this specification.WS-Events defines an event as a change in the state of a resource or request for processing. The specification describes three main entities. The event producer is an entity which generates notifications. These notifications are received by the event consumers. The event broker is responsible for routing the notifications. Brokers typically aggregate and publish events from several producers. An event broker can also apply some transformation to the notifications it processes. The precise role of the broker remains unclear in WS-events. Subscription requests and notifications are described as (direct) messages between the event producer and the event consumer.The specification does not provide descriptions of entities responsible for subscription or subscription management tasks (such as the subscriber and subscription manager in WS-Notification and WS-Eventing) nor does it distinguish between publisher and producer roles (as in WS-Brokered Notification).The WS-Eventing specification describes a protocol that allows Web services to subscribe to or accept subscriptions for event notification messages. The specification defines four entities in the event notification architecture