Whenever Discover, the KDE App manager starts, it shows this message:

Please make sure that Appstream is properly set up on your system.

Wikipedia tells me that:

AppStream is an agreement between major Linux vendors (i.e. Red Hat, Canonical, SUSE, Debian, Mandriva, etc.) to create an infrastructure for application installers on Linux and sharing of metadata.

but there's little more on the web.

Discover seems to run just fine.

How can I verify that Appstream is set up properly? If not, how can the installation be fixed?

Thanks - jon