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Hierarchical MQTT Eventing

Hierarchical MQTT Eventing#

User Story & Use Case#

As AAS Components user

I want hierarchical MQTT topics in the AAS Server Component

so that I can subscribe precisely to the topics of interest without having to filter on client side

MQTT supports hierarchical topics with wildcard subscription support. For example, if the topics a/b/x and a/b/y exist, subscribing to a/b/+ subscribes to all events broadcasted on both topics.

Please note, that this feature can not be combined with lambda properties due to them being only updated on query.

Feature Overview#

The following hierarchical topics with their respective payloads are implemented:

  • aas-repository//shells/created

    • Payload: Complete AAS (without ConceptDictionaries)

  • aas-repository//shells/deleted

    • Payload: Complete AAS (old, without ConceptDictionaries)

  • aas-repository//shells/updated

    • Payload: Complete AAS (without ConceptDictionaries)

  • aas-repository//shells//submodels/created

    • Payload: Submodels without SMEs

  • aas-repository//shells//submodels/deleted

    • Payload: Submodels without SMEs

  • aas-repository//shells//submodels/updated

    • Payload: Submodels without SMEs

  • aas-repository//shells//submodels//submodelElements//created

    • Payload: SME without value (or value-equivalent)

  • aas-repository//shells//submodels//submodelElements//deleted

    • Payload: old SME without value (or value-equivalent)

  • aas-repository//shells//submodels//submodelElements//updated

    • Payload: SME without value (or value-equivalent)

  • aas-repository//shells//submodels//submodelElements//value

    • SME value, if not specified otherwise via qualifier

For AAS/SM-Identifier encoding, Base64URL encoding and URL encoding are available.

Feature Configuration#

The feature can be configured in the aas.properties file by setting aas.events = MQTTV2 for Base64URL encoding or aas.events = MQTTV2_SIMPLE_ENCODING for URL encoding. Additionally, the repo id needs to be configured via aas.id = .

An example configuration for this feature could be:

aas.events = MQTTV2
aas.id = product-aas-repo

The MQTT broker connectivity is configured via mqtt.properties

Additional to the overall event configuration, the payload send on the ../value topic for updating a SubmodelElement’s value can be tailored. For SubmodelElements containing huge values like Blobs, it may be sensible to disable sending their value’s content. If this is the case, a qualifier with type emptyValueUpdateEvent and value set to true will configure empty value updates for the specific SubmodelElement (cf. ObservableSubmodelAPIV2Helper).

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