def urn(self):
        """
        MobID Uniform Resource Name representation.
        https://en.wikipedia.org/wiki/Uniform_Resource_Name
        """

        SMPTELabel = self.SMPTELabel
        Data4 = self.Data4

        # handle case UMIDs where the material number is half swapped
        if (SMPTELabel[11] == 0x00 and
            Data4[0] == 0x06 and Data4[1] == 0x0E and
            Data4[2] == 0x2B and Data4[3] == 0x34 and
            Data4[4] == 0x7F and Data4[5] == 0x7F):

            # print("case 1")
            f = "urn:smpte:umid:%02x%02x%02x%02x.%02x%02x%02x%02x.%02x%02x%02x%02x." + \
             "%02x"  + \
             "%02x%02x%02x." + \
             "%02x%02x%02x%02x.%02x%02x%02x%02x.%08x.%04x%04x"

            return f % (
                 SMPTELabel[0], SMPTELabel[1], SMPTELabel[2],  SMPTELabel[3],
                 SMPTELabel[4], SMPTELabel[5], SMPTELabel[6],  SMPTELabel[7],
                 SMPTELabel[8], SMPTELabel[9], SMPTELabel[10], SMPTELabel[11],
                 self.length,
                 self.instanceHigh, self.instanceMid, self.instanceLow,
                 Data4[0], Data4[1], Data4[2], Data4[3],
                 Data4[4], Data4[5], Data4[6], Data4[7],
                 self.Data1, self.Data2, self.Data3)
        else:
            # print("case 2")
            f = "urn:smpte:umid:%02x%02x%02x%02x.%02x%02x%02x%02x.%02x%02x%02x%02x." + \
             "%02x"  + \
             "%02x%02x%02x." + \
             "%08x.%04x%04x.%02x%02x%02x%02x.%02x%02x%02x%02x"

            return f % (
                 SMPTELabel[0], SMPTELabel[1], SMPTELabel[2],  SMPTELabel[3],
                 SMPTELabel[4], SMPTELabel[5], SMPTELabel[6],  SMPTELabel[7],
                 SMPTELabel[8], SMPTELabel[9], SMPTELabel[10], SMPTELabel[11],
                 self.length,
                 self.instanceHigh, self.instanceMid, self.instanceLow,
                 self.Data1, self.Data2, self.Data3,
                 Data4[0], Data4[1], Data4[2], Data4[3],
                 Data4[4], Data4[5], Data4[6], Data4[7])
MobID Uniform Resource Name representation.
        https://en.wikipedia.org/wiki/Uniform_Resource_Name