UUID格式：8-4-4-4-12 - 爲什麼？

Question

爲什麼UUID以格式「8-4-4-4-12」（數字）顯示？我已經查明瞭原因，但無法找到需要它的決定。格式化爲十六進制字符串UUID的

示例： 58D5E212-165B-4CA0-909B-C86B9CEE0111

Answer 1

它由time, version, clock_seq_hi, clock_seq_lo, node分離，如在RFC followoing指示。

從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)       | 
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 

Answer 2

格式在IETF RFC4122在第3節所定義的輸出格式定義它說： 「UUID = ...」

3.-命名空間登記模板

命名空間ID：UUID註冊信息： 註冊日期：2003-10-01

JTC 1/SC6（ASN.1報告人組）

句法結構的聲明：：210

聲明的名稱空間的註冊 甲UUID是一個標識符，是跨越空間和時間兩者， 獨特相對於所述所有UUID的空間。由於UUID的大小是固定的，並且包含時間字段，所以可能出現 翻轉的值（在A.D. 3400附近，取決於所使用的特定算法 ）。 UUID可以用於多種目的，從標記生命期很短的對象到可靠地識別網絡中持久性很高的對象 。

The internal representation of a UUID is a specific sequence of 
    bits in memory, as described in Section 4. To accurately 
    represent a UUID as a URN, it is necessary to convert the bit 
    sequence to a string representation. 

    Each field is treated as an integer and has its value printed as a 
    zero-filled hexadecimal digit string with the most significant 
    digit first. The hexadecimal values "a" through "f" are output as 
    lower case characters and are case insensitive on input. 

    The formal definition of the UUID string representation is 
    provided by the following ABNF [7]: 

    UUID     = time-low "-" time-mid "-" 
          time-high-and-version "-" 
          clock-seq-and-reserved 
          clock-seq-low "-" node 
    time-low    = 4hexOctet 
    time-mid    = 2hexOctet 
    time-high-and-version = 2hexOctet 
    clock-seq-and-reserved = hexOctet 
    clock-seq-low   = hexOctet 
    node     = 6hexOctet 
    hexOctet    = hexDigit hexDigit 
    hexDigit = 
     "0"/"1"/"2"/"3"/"4"/"5"/"6"/"7"/"8"/"9"/
     "a"/"b"/"c"/"d"/"e"/"f"/
     "A"/"B"/"C"/"D"/"E"/"F"