PackageKit purpose?

[Timothy Murphy]

What exactly is the purpose of PackageKit?
Is it essential?
It is used by yum in some way?

I'm asking because I get an error message
-------------------------------
Fetch Job Error - Plasma Desktop Shell

Unknown error. (Unable to fetch item from backend)
-------------------------------
whenever I login or wake from hibernation,
and I saw somewhere a suggestion that this might be
related to PackageKit.

-- 
Timothy Murphy  
e-mail: gayleard /at/ eircom.net
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College Dublin