that would be a v4 uuid, like you asked for in the above code.
test=# select uuid_generate_v4();
uuid_generate_v4
--------------------------------------
09b24e5b-5116-435e-94b9-f0da4661f594
afaik, all UUID's are 128 bit numbers expressed in hexadecimal in that format. This is an ISO standard.
--
john r pierce, recycling bits in santa cruz