Request Open: July 2, 2025 5:58 pm — August 1, 2025 12:00 am (22 days left) (AoE)
02 July, 2025: The Open Geospatial Consortium (OGC) is seeking public comment on the candidate OGC SensorThings API Extension: WebSub Asynchronous Messaging Standard (STA-WebSub). The comment period is open for 30 days and will close on August 1, 2025.
The candidate standard defines an additional capability for the OGC SensorThings API that enables the distribution of updates via HTTP(S), as defined in the W3C WebSub Recommendation.
The STA-WebSub system follows the W3C WebSub architecture, consisting of a Subscriber, Hub, and Publisher, where the Publisher can be split into two components (the HTTP interface of the SensorThings API service and the MQTT broker).
Since the only change to the SensorThings API service involves support for WebSub discovery, this extension focusses solely on defining the requirements for the HTTP interface to implement the W3C WebSub Discovery protocol.
Subscribers can fetch sensor data (observations) from a SensorThings API service and use the same URL to subscribe for updates. This eliminates the need for polling, as any updates to the data, based on the subscribed URL, are automatically submitted to the subscriber’s webhook when triggered.
This WebSub extension is easy to integrate into existing systems, as producers only need to set up a W3C WebSub compliant Hub that receives subscription updates via MQTT. Consumers only need to set up a WebSub Subscriber to receive updates through WebHook. The SensorThings API MQTT protocol remains internal and does not need to be exposed to the subscriber.
Any SensorThings API service that extends the MQTT topic pattern to include filter and expand capabilities using ODATA query parameters allows subscribers to define triggering conditions using $filter. Using the ODATA query parameters $select and $expand also supports subscribers to receive data that is precisely structured and scoped to their needs.
The STA-WebSub extension improves the flexibility of using a SensorThings API service for building asynchronous workflows. By allowing users to define the triggering conditions and customize the event data structure pushed via HTTP(S) POST to the WebHook, this extension supports fit-for-purpose event processing. Access control can be implemented in the discovery functionality which controls the subscription based on business or access control policies.
TO COMMENT
The candidate OGC SensorThings API Extension: WebSub Asynchronous Messaging Standard (STA-WebSub) is available for review and comment on the OGC Portal. Comments can be submitted to a dedicated email reflector for a period ending on the “Close request date” listed above. Comments received will be consolidated and reviewed by OGC members for incorporation into the document. Please submit your comments via this email address, using this Comments Template for the message body.
About OGC
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