This is from a changelog of yum-3.2.28-16.fc15:
* Tue Jan 04 2011 Seth Vidal <skvidal at fedoraproject.org> -
* 3.2.28-15
- latest head
- conflicts zif
That indeed conflicts and if zif is present it blocks an update
of yum.
Only that "Zif is a simple yum-compatible library ..." and it
was pulled in the past through dependencies by some past update
of yum or maybe PackageKit. Shouldn't yum-3.2.28-16.fc15 obsolete
that instead if no longer needed? It appears that zif-0.1.3-3.fc15
is indeed not used anymore (or, at least, nothing has dependencies
on it).
Michal