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Hello Kai.
The purpose was to give some structure to the MQTT payload.
The timestamp and the GPS position are promoted to top level metadata for the payload because of being so commonly used.
KuraMetrics can be seen as strongly typed properties for the payload.
KuraMetrics are generally used to capture some of the telemetry data (e.g. temperature reading, passenger counts, …).
Through this simple structure, applications consuming the message can extract single data points simply using the metric name, write message filters or data stream rules, or design a generic simple storage scheme.
The Kura Payload body is generally opaque and its structure and usage is application specific.
It can be used for large binary information (e.g. an image) or for application-specific encoded data that is attached to the message.
The design was largely inspired by the JMS BytesMessage class.
The JMS Message headers in Kura are limited to the timestamp and position.
The JMS Message strongly-typed properties are represented by the KuraMetrics.
The JMS BytesMessage body is represented by the body filed in the KuraPayload.
It is also worth mentioning that Google Protocol Buffer messages are extensible; more strongly-typed attributes can be added into the payload yet retaining the basic structure.
Hope this helps.
-Marco
Hi Marco,
Thanks for sharing this J Taking
a first look at the message definitions, I have a hard time understanding what the purpose of the KuraMetric type compared to the body is. Can you elaborate a little on this?
following up our conversion at EclipseCON, please find below the definition of the MQTT payload adopted by Kura.
It is based on Google Protocol Buffers so it offers an efficient serialization while being language independent.
Its main purpose is to describe structure not semantics; it leaves rooms of extensibility for specific vertical applications.
The Java Class wrapping the payload is available here:
- Introduction
of new members
- Follow-up
on action items from Face-2-Face meeting
o Support for different
protocols
o Common message
formats for MQTT
- December
announcement for project releases (Concierge, Kura, OM2M and SmartHome)
- Community
outreach at Embedded World Germany
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