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- Q: What is Sparkplug in a nutshell?
- A: Sparkplug is a set of definitions on top of MQTT to serve the following purposes:
- Define a set of topics to ensure state/quality of data be ensured in a backend MQTT client application
- Define a standard payload format that allows an edge node/device client to communicated with a backend application
- Define a flow of messages to ensure the state/quality of data.
- A: Sparkplug is a set of definitions on top of MQTT to serve the following purposes:
- Q: What is the difference between Sparkplug A and Sparkplug B?
- A: The 'A' and 'B' qualifiers differentiate payload encoding formats. The following points show the similarities and differences between the two:
- Important note! Sparkplug A has been deprecated and any new projects being created should use Sparkplug B. If you need a copy of the Sparkplug A specification you can contact support@cirrus-link.com to get a copy.
- Both A and B use the same topic format with a qualifier as the first token in the topic namespace to denote the payload encoding format
- The message flow of both A and B is the same
- The only difference is the payload encoding format.
- Both formats are open source
- Both are based on Google Protobuf definitions
- Sparkplug A uses Eclipse Kura's payload definition found here: https://raw.githubusercontent.com/eclipse/kura/develop/kura/org.eclipse.kura.core.cloud/src/main/protobuf/kurapayload.proto
- Sparkplug B uses an expanded definition allowing for more metadata found here: https://raw.githubusercontent.com/Cirrus-Link/Sparkplug/master/sparkplug_b/sparkplug_b.proto
- A: The 'A' and 'B' qualifiers differentiate payload encoding formats. The following points show the similarities and differences between the two:
- Q: What is the difference between a Template definition and instance?
- A: There are two parts to a Template
- Template Definition
- This metric will will contain all the member Metrics with their default values/properties, as well as any Parameters with their default values. This metric is always only published in the NBIRTH message
- Template Instance
- This metric is one or more "instances" of the above definition. It will contain the any member metrics with values/properties that are overridden/different from the defaults in the Template Definition. They are published as you would normal tags (BIRTH/DATA/CMD). When published in a NDATA/DDATA/NCMD/DCMD message they may only contain a subset of the member Metrics (if those are the only values that have changed)
- Other template fields
- is_definition
- true for a Template Definition metric, false for a Template Instance Metric
- template_ref
- This is used by a Template Instance to specify the "name" of the Template Definition
- is_historical
- Used to mark a Template Instance (or any Metric) as a historical (rather than a live) value. MQTT Engine may handle historical Metrics differently depending on how it is configured (see MQTT Engine documentation)
- is_transient
- Not currently used, will be ignored by MQTT Engine, can be omitted or set to false
version
Not currently used, will be ignored by MQTT Engine, can be omitted or set to null
- is_definition
This template_samples.txt contains some sample template structures (in JSON) as well as some Java code for creating a Template. These should help show the basic Template structure and contain the important fields of a Template Definition and Instance. However, they are just references expressed in JSON, not actual protobuf representations (which may be a bit more verbose)
- Template Definition
- A: There are two parts to a Template
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