Something

def installParcel(parcel, oldVersion=None):
    ...
    publishedFreeBusy = UnionCollection.update(parcel, 'publishedFreeBusy')
    unpublishedFreeBusy = DifferenceCollection(parcel, "unpublishedFreeBusy",
        sources=[schema.ns('osaf.pim', parcel.itsView).allEventsCollection, publishedFreeBusy]
    )