MQTT Eventing

The AAS Repository can publish hierarchical MQTT events for repository operations and operations on an individual Asset Administration Shell.

Warning

Starting with BaSyx Java Server SDK Milestone 14, MQTT uses canonical topics with unpadded UTF-8 Base64URL-encoded identifier segments. Submodel-reference topics no longer contain the raw submodel identifier, and AAS service topics no longer contain a raw or URL-percent-encoded shell identifier.

This is a breaking subscription change. Events are not also published on the legacy topics, so existing subscribers must update their topic filters when upgrading to Milestone 14.

Configuration

Enable MQTT eventing in the standalone AAS Repository component with:

basyx.aasrepository.feature.mqtt.enabled=true
mqtt.clientId=aas-repository
mqtt.hostname=localhost
mqtt.port=1883

mqtt.clientId must be unique among clients connected to the broker. The connection scheme defaults to tcp. The complete connection configuration is:

Property	Required	Default	Description
mqtt.clientId	Yes	-	MQTT client identifier
mqtt.hostname	Yes	-	MQTT broker host name
mqtt.port	Yes	-	MQTT broker port
mqtt.protocol	No	tcp	Connection URI scheme, for example tcp or ws
mqtt.username	No	Empty	Broker user name
mqtt.password	No	Empty	Broker password

Credentials are applied only when both mqtt.username and mqtt.password are set. Automatic reconnect is enabled.

The available feature switches are:

Property	Events enabled
basyx.aasrepository.feature.mqtt.enabled=true	AAS repository events; this module is included in the standalone AAS Repository component
basyx.aasservice.feature.mqtt.enabled=true	Events for operations on an individual AAS; add basyx.aasservice-feature-mqtt when composing a custom SDK application
basyx.feature.mqtt.enabled=true	Every MQTT feature available on the application’s classpath

Topic placeholders

Placeholder	Meaning
$repoId	Repository name configured with basyx.aasrepo.name; it is not encoded
$shellIdBase64Url	AAS identifier encoded as unpadded UTF-8 Base64URL
$submodelIdBase64Url	Submodel identifier encoded as unpadded UTF-8 Base64URL

For example, the identifier https://example.com/aas/1 becomes aHR0cHM6Ly9leGFtcGxlLmNvbS9hYXMvMQ. Base64URL uses - and _ instead of + and / and omits trailing = padding.

AAS repository events

Event	Topic	Payload
AAS created	aas-repository/$repoId/shells/created	Created AAS JSON
AAS updated	aas-repository/$repoId/shells/updated	Updated AAS JSON
AAS deleted	aas-repository/$repoId/shells/deleted	Deleted AAS JSON
Submodel reference created	aas-repository/$repoId/shells/submodels/$submodelIdBase64Url/created	Created AAS JSON
Submodel reference deleted	aas-repository/$repoId/shells/submodels/$submodelIdBase64Url/deleted	Deleted AAS JSON

AAS service events

These events are provided by the Java SDK’s basyx.aasservice-feature-mqtt module. When composing a custom application with this module, enable it with basyx.aasservice.feature.mqtt.enabled=true or the global switch described above. The module is not bundled in the standalone AAS Repository component.

Event	Topic	Payload
Asset information set	aas-repository/$repoId/shells/$shellIdBase64Url/assetInformation/updated	Updated AssetInformation JSON
Submodel reference added	aas-repository/$repoId/shells/$shellIdBase64Url/submodelReferences/created	Created SubmodelReference JSON
Submodel reference removed	aas-repository/$repoId/shells/$shellIdBase64Url/submodelReferences/deleted	Deleted SubmodelReference JSON

Milestone 14 migration

Event	Before Milestone 14	Starting with Milestone 14
Repository submodel-reference create/delete	Raw submodel ID in the topic	$submodelIdBase64Url
AAS service operations	Raw or URL-percent-encoded shell ID	$shellIdBase64Url

Repository names remain unchanged. A broad subscriber can use aas-repository/$repoId/#; consumers that parse identifier segments must Base64URL-decode the relevant segment as UTF-8.