Spec is misleading when it comes to "known" metrics.

[SeppPenner]

Check

6.4.19. NBIRTH
The NBIRTH is responsible for informing host applications of all of the information about the Edge
Node. This includes every metric it will publish data for in the future.

6.4.20. DBIRTH
The DBIRTH is responsible for informing the Host Application of all of the information about the
device. This includes every metric it will publish data for in the future.

--> All metrics need to be known in DBIRTH / NBIRTH already?

5.15
There are other reasons a Host Application may send out Node Control/Rebirth NCMD messages.
These include but are not limited to:
◦ Receiving any DBIRTH, NDATA, DDATA, or DDEATH before receiving an NBIRTH from a
Sparkplug Edge Node
◦ Receiving a metric in an NDATA message that was not included in the previous NBIRTH
message
◦ Receiving a metric in a DDATA message that was not included in the previous DBIRTH message
◦ Receiving an alias value that was not included in the corresponding NBIRTH or DBIRTH

But still, metrics can be new from DDATA or NDATA messages? How do these requirements fit together?

[SeppPenner]

Or is it meant to be used like this?

Imagine a scenario with one library and another one that speak Sparkplug. Let's say the other library allows to send unknown metrics on NDATA or DDATA --> Theoretically, my library would need to tell these nodes to do a rebirth because the metrics are unknown.

[ArFe]

I'm not sure I understand your question. Known means known. If you send an NDATA/DDATA with a new Metric, that would be invalid and the Host Application will require you to send a new NBIRTH/DBIRTH that contains your new Metric in order to move forward. Your Node/Device will be set as offline until you send an appropriate NBIRTH/DBIRTH.

In other words, sending an NDATA/DDATA with a new metric is wrong and should not be done.

What exactly is not clear?

PS.: I don't think this is the appropriate channel to discuss the Sparkplug B specs

[SeppPenner]

@ArFe Thank you for the clearification. I just had the question within my project several times. Need to check it, so keep it open for now :)