原文地址：http://blog.csdn.net/nidehong/archive/2006/11/22/1406125.aspx
UUID
通用惟一標識符（UUID）是128位比特的數字，用來惟一地標識因特網上的某些對象或者實體。
A Universally Unique Identifier is an identifier standard used in software construction, standardized by the Open Software Foundation (OSF) as part of the Distributed Computing Environment (DCE). The intent of UUIDs is to enable distributed systems to uniquely identify information without significant central coordination. Thus, anyone can create a UUID and use it to identify something with reasonable confidence that the identifier will never be unintentionally used by anyone for anything else. Information labelled with UUIDs can therefore be later combined into a single database without need to resolve name conflicts. The most widespread use of this standard is in Microsoft's Globally Unique Identifiers (GUIDs) which implement this standard.
一個UUID 是一個標識符標準用于軟件架構，是由開放軟件基金會（OSF）作為分布式計算環境（DCE）的一部分而制定的標準。UUIDs的目的就是使分布式系統可以不需要重要的中央調合系統而能唯一地標識信息。這樣，任何人能創造一個UUID 和使用它來標識一些東西，而且，你有足夠的信心來確定這個標識是永遠不會被任何人無意地使用在任何東西上。因此，信息加上了UUID標簽就能合并到單個數據庫中而不用去解決命名沖突的問題。這個標準的廣泛應用在微軟的全球唯一標識符（GUIDs）上，GUID實現了這個標準。
A UUID is essentially a 16-byte number and in its canonical form a UUID may look like this:
:550E8400-E29B-11D4-A716-446655440000
And has this structure in the C programming language:
typedef struct {
unsigned32 time_low;
unsigned16 time_mid;
unsigned16 time_hi_and_version;
unsigned8 clock_seq_hi_and_reserved;
unsigned8 clock_seq_low;
byte node6;
} uuid_t;
The J2SE 5.0 release of Java provides a class that will produce 128-bit UUIDs. The API documentation for the class refers to ISO/IEC 11578:1996.
關于UUID的定義，詳細內容可參考http://www.ietf.org/rfc/rfc4122.txt，文檔里面還有C語言對UUID標準的各種實現。
GUID
A Globally Unique Identifier or GUID is a pseudo-random number used in software applications. While each generated GUID is not guaranteed to be unique, the total number of unique keys (2128 or 3.4028×1038) is so large that the possibility of the same number being generated twice is very small.
一個全球唯一標識符 或 GUID 是一個假隨機數用于軟件中。雖然每個產生的GUID是不保證唯一的，但不同的標識符總數是（2128 也就是3.4028×1038）如此之大，以至于相同的數字被產生兩次的機率是很相當小的。
The GUID is an implementation by Microsoft of a standard called Universally Unique Identifier (UUID), specified by the Open Software Foundation (OSF).
GUID 是微軟對UUID這個標準的實現。UUID是由開放軟件基金會（OSF）定義的。
UUID還有其它各種實現，不止GUID一種，其它的在此不詳細說明。