Introduction Realization of Publish Subscribe

66 Copyright © 2010 Open Geospatial Consortium, Inc.

6.5.2.2 Considerations on the Notify Message sent via HTTP

The Notify operation is used to send notifications to consumers. Usually, no response is expected from the consumer upon receipt of this message. However if HTTP is used as underlying protocol each SOAP request sent via HTTP automatically has an HTTP response. The Web Services Interoperability Organization has some recommendations for SOAP-via-HTTP communication 3 . Especially section 3.8.3 on status codes is interesting as it defines the success status codes for HTTP responses. As the HTTP specification [1] defines that a 200 OK response shall contain a message body while 202 Accepted should contain a message body and is intended to signal the acceptance of a process we recommend using 204 No Content as response code – this status code requires that no content is provided in the response body. This fulfills the semantics of the Notify response best and is within the recommendation of WS-I which states that “An INSTANCE MUST use a 2xx HTTP status code on a respo nse message that indicates the successful outcome of a HTTP request.” It also does not conflict with the HTTP defined semantics of the status codes. The response should not contain a body payload. Consequently, every publisher should be implemented to accept all 2xx codes as notify response. NOTE: Usage of WS-ReliableMessaging results in at least some content communicated back to the entity that sent the notification in a reliable way.

6.5.3 Summary

Chapter 6.5 documents how well a given publish subscribe technology supports the requirements derived from the abstract model. During the testbed, the participants were able to establish the mapping for one realization technology, namely WS-Notification – the results are documented in section 6.5.2.1. WS-Notification was already used in OWS- 6 and was in OWS-7 also applied in the Aviation and SFE threads. Other technologies, like Atom AtomPub, WS-Eventing etc. can and should in the future also be investigated in this way. The foundation for that work is laid in this report. When more technology mappings for the requirements have been achieved, a meaningful comparison of the different technologies can be made. That study will point out which technology is most appropriate for realizing publish subscribe functionality required by OGC services per given OWS binding style SOAP, RESTful etc. 3 http:www.ws-i.orgProfilesBasicProfile-2_028WGD29.htmlSOAPHTTP