Why are UUID's presented in the format "8-4-4-4-12" (digits)? I've had a look around for the reason but can't find the decision that calls for it.
Example of UUID formatted as hex string: 58D5E212-165B-4CA0-909B-C86B9CEE0111
It's separated by time, version, clock_seq_hi, clock_seq_lo, node, as indicated in the following RFC.
From the IETF RFC4122:
4.1.2. Layout and Byte Order
To minimize confusion about bit assignments within octets, the UUID
record definition is defined only in terms of fields that are
integral numbers of octets. The fields are presented with the most
significant one first.
Field Data Type Octet Note
#
time_low unsigned 32 0-3 The low field of the
bit integer timestamp
time_mid unsigned 16 4-5 The middle field of the
bit integer timestamp
time_hi_and_version unsigned 16 6-7 The high field of the
bit integer timestamp multiplexed
with the version number
clock_seq_hi_and_rese unsigned 8 8 The high field of the
rved bit integer clock sequence
multiplexed with the
variant
clock_seq_low unsigned 8 9 The low field of the
bit integer clock sequence
node unsigned 48 10-15 The spatially unique
bit integer node identifier
In the absence of explicit application or presentation protocol
specification to the contrary, a UUID is encoded as a 128-bit object,
as follows:
The fields are encoded as 16 octets, with the sizes and order of the
fields defined above, and with each field encoded with the Most
Significant Byte first (known as network byte order). Note that the
field names, particularly for multiplexed fields, follow historical
practice.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| time_low |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| time_mid | time_hi_and_version |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|clk_seq_hi_res | clk_seq_low | node (0-1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| node (2-5) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+