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Universally Unique IdentifierA 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 that 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. A UUID is essentially a 16-byte number and in its canonical form a UUID may look like this: - 550E8400-E29B-11D4-A716-446655440000
UUIDs are documented as part of ISO/IEC 11578:1996 "Information technology -- Open Systems Interconnection -- Remote Procedure Call (RPC)" There are efforts underway to document UUIDs as a separate standard through the ISO (ISO/IEC FDIS 9834-8), and through the IETF. The most recent Internet Draft for a RFC was submitted in December 2004 and expires in June 2005. Conceptually, the original (version 1) generation scheme for UUIDs was to concatenate the UUID version with the MAC address of the computer that is generating the UUID, and with the number of 100-nanosecond intervals since the adoption of the Gregorian calendar. In practice, the actual algorithm is more complicated. This scheme has been criticized in that it is not sufficiently 'opaque'; it reveals both the identity computer that generated the UUID and the time at which it did so. Several other generation algorithms have been developed and incorporated into the standard, including a scheme relying only on random numbers (version 4 UUIDs), and a scheme deriving a UUID from a URL via MD5 (version 3 UUIDs) or SHA-1 (version 5 UUIDs) hashing. See also External links
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