Handling a Pausable Subscription

Copyright © 2010 Open Geospatial Consortium, Inc. 45

6.2.2.4 Sending a Notification

One of the most important activities in a publish subscribe system is to actually send notifications. Figure 18 shows the activity of publishing an event. A Notify event message is emitted and sent to some not further specified system entity. Publish Notify Figure 18: Publishing Activity The activity relies upon the interface defined in section 6.2.1.4.11.

6.2.2.5 Handling a Notification at a Broker

A broker is capable of receiving incoming notifications and matching them against existing subscriptions. Each notification matching a subscription’s filter criteria needs to be published to endpoint defined for that subscription. The following diagram shows the activities and events involved in handling an incoming notification at a broker. The activities of the publisher and broker run in parallel. 46 Copyright © 2010 Open Geospatial Consortium, Inc. P u b li s h e r :P u b li s h e r B ro k e r :B ro k e r Notify Broker Notify Notify Handle notification Perform filter check Not matching Publish Publish Stop Stop [otherwise] [deliveryToChannel defined] [otherwise] [otherwise] [Notification matches] [deliveryTo defined and subscription not paused] Figure 19: Notification Handling Activity A publisher notifies a broker by emitting a Notify event message which is sent to the broker. As no response which would be a related event is expected by the publisher, its activity terminates after the notification has been sent. When receiving a Notify event message, the broker checks the filter of each subscription it manages against the event. If the event matches, the broker publishes it. In case that a deliveryTo endpoint is defined and the subscription is not paused, the event is published to the deliveryTo endpoint. If the deliveryToChannel is set in the subscription, the event is published to that endpoint. Note that at least one of these delivery endpoints shall be defined for each subscription. When the matching and publication was performed the handling of the notification for a specific subscription stops.

6.2.2.6 Registering a New Publisher

A new event source can be registered at an Event Service Broker as new publisher. The interactions involved in creating and managing a registration and publication are shown in the following sequence diagram.