def check_origin(self):
        """Do some simple checking of the zone's origin.

        @raises dns.zone.NoSOA: there is no SOA RR
        @raises dns.zone.NoNS: there is no NS RRset
        @raises KeyError: there is no origin node
        """
        if self.relativize:
            name = dns.name.empty
        else:
            name = self.origin
        if self.get_rdataset(name, dns.rdatatype.SOA) is None:
            raise NoSOA
        if self.get_rdataset(name, dns.rdatatype.NS) is None:
            raise NoNS