Applying HP patches

[zedude]

Hi,

I know it may be a dumb question but i'm quite new in managing HP servers
So i have 2 general questions about applying HP patch :

* is there a way to control the patch has not already been applied ? Does an installed patch is visible in the add/remove prg the way windows patches are done ?

* when you want to apply a patch, is there a way to rollback if there's any trouble ? Is there an exe or procedure to de-installed the patches ?

Thanks very much for any answers