Have not found any code examples of how to set upstream projects. Neither
does it seems possible with the Jenkins API.
I tried to add directly in config.xml
myLib++
myLib2++
But it didn't take.
According to both JSON and XML schema both downstreamProject and
upstreamProject should be possible.
Upstream means a project is kind of above of some others in the build
lifecycle. See it as a waterfall if you like, and water in a waterfall goes
down (more rarely up ;-)).
You also must think of the required building order: to build your final
artifact(s). In your case, you must indeed have built
