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WS Notification and WS Topics in the WS Resources Framework


This article continues our discussion of the WS-Resource Framework, a set of proposed standards that formalizes the relationship between Web services and state. In this part, the third of a multi-part series, we cover the use of notifications and topics. It is excerpted from chapter 8 of the book Building Web Services with Java: Making sense of XML, SOAP, WSDL, and UDDI, written by Steve Graham et al. (Sams; ISBN: 0672326418).

Author Info:
By: Sams Publishing
Rating: 5 stars5 stars5 stars5 stars5 stars / 6
July 13, 2006
TABLE OF CONTENTS:
  1. · WS Notification and WS Topics in the WS Resources Framework
  2. · Subscribing for Notification
  3. · The Subscription WS-Resource
  4. · Topics and Topic Spaces
  5. · TopicPathExpressions
  6. · Rounding Out the XML Model of Topics: aliasRef

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WS Notification and WS Topics in the WS Resources Framework - The Subscription WS-Resource
(Page 3 of 6 )

WS-Notification models a subscription as a WS-Resource. The subscription is a stateful resource that is created by a subscribe request and that uses operations defined by WS-ResourceLifetime (see the section "Resource Lifetime") to manage the lifetime of the subscription.

The Subscription WS-Resource is associated with a Web service implementing the SubscriptionManager portType. This portType defines a collection of resource properties corresponding to the components in the subscribe request, allowing the requestor to use WS-ResourceProperties operations to read and write the values of subscription-related resource properties. This portType also defines a creationTime resource property that records when the subscription was created.

The SubscriptionManager also supports operations defined by WS-ResourceLifetime, to give requestors the ability to terminate the resource. So, for example, if The Skateboard Warehouse was no longer interested in notifications associated with their PurchaseOrder WS-Resource, they could send a destroy operation to the SubscriptionManager (remembering to use the implied resource pattern to identify the subscription WS-Resource). Of course, the requestor may also use the time-based or scheduled termination mechanism specified by WS-ResourceLifetime to manage the lifetime of the subscription resource.

The complete collection of resource properties defined by a Subscription WS-Resource is as follows:

  • ConsumerReference—The EPR to the consumer that receives notification messages associated with this subscription.

  • TopicExpression—The expression that indicates the set of topics associated with this subscription.

  • UseNotify—Determines if the notification message is sent with additional meta-data.

  • Precondition—The precondition associated with the subscription.

  • Selector—The selector or filter associated with the subscription.

  • SubscriptionPolicy—The policies associated with the subscription.

  • CreationTime—The time the subscription was created.

  • CurrentTime, TerminationTime—Defined by WS-ResourceLifetime. These resource properties describe the lifetime of a subscription.

Note that most of the values of these resource properties are derived from the subscribe request message. A requestor would use operations defined by WS-ResourceProperties (included as part of the SubscriptionManager portType) to read and write the values of these resource properties.

The SubscriptionManager portType also defines a pauseSubscription operation and a resumeSubscription operation. These operations work to stop and restart the process of sending notification messages to the notification consumer based on this subscription. If a requestor wishes to temporarily halt the sending of notification messages based on this subscription, it sends a pauseSubscription request message to the SubscriptionManager Web service associated with the subscription. To resume sending messages, the requestor sends a resumeSubscription request.


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