Why did you define features for all the drivers as well? Wouldn't it be good enough to add the bundle to the persistence service features above?

JPA Persistence, will use the drivers later too. So I externalized them (the user doesn`t see them, or is it?). If we load them all by default, this would cause over 15 MB Traffic.

JPA Persistence, will use the drivers later too

Ok, but as long as the feature only includes a single bundle, you can also reference the single bundle in the JPA Persistence and do not necessarily require a feature. A feature mainly makes sense, if you need to package multiple bundles and/or additional resources or configurations with it.

the user doesn`t see them

Correct, the will only be visible in the shell when listing available features. But that's ok.

If we load them all by default, this would cause over 15 MB Traffic.

This was anyhow not my suggestion. I simply meant you could also do a

    <feature name="openhab-persistence-jdbc-derby" description="JDBC Persistence Apache Derby" version="${project.version}">
         <configfile finalname="${openhab.conf}/services/jdbc.cfg" override="false">mvn:${project.groupId}/openhab-addons-external/${project.version}/cfg/jdbc</configfile>
         <feature prerequisite="false" dependency="false">openhab-runtime-base</feature>
         <feature prerequisite="false" dependency="false">openhab-runtime-compat1x</feature>
         <bundle start-level="80">mvn:org.apache.derby/derbyclient/10.12.1.1</bundle>
         <bundle start-level="80">mvn:org.openhab.persistence/org.openhab.persistence.jdbc/${project.version}</bundle>
     </feature>

I understand, will change it.

If you plan to reuse the bundles, it might also be a good idea to put the version of the drivers as a property into the pom.xml and only refer to it here - then you can change it later at a single place and it will be picked up by JDBC and JPA persistence likewise.

It should probably go best in here (all of them): https://github.com/openhab/openhab/blob/master/features/openhab-addons/pom.xml
And I would call the property simply ${derby.version}.

Alternatively, you could put it in the parent pom, this is how it looks for the openhab2-addons: https://github.com/openhab/openhab2-addons/blob/master/pom.xml#L50

OK, then all bundles in openHAB can use the same version of the driver later.
This has advantages for compatibility and stability?!

Can this variable from parent pom used too in local https://github.com/lewie/openhab/blob/add_jdbc_to_paperui_and_features/bundles/persistence/org.openhab.persistence.jdbc/pom.xml as ${derby.version}? If yes, I can delete it (them all) there.

Yes, exactly! I wasn't aware that you need it there anyhow already - then the root pom is indeed the best place as it is shared between the bundles and the features.

Thank You!

Anything went wrong with my comment wrong document, don' know...
That I can go on, please can you give me a short state about that too:
lewie@7aee28d#commitcomment-16098127