A UUID (Universal Unique Identifier) is a 128-bit number used to uniquely identify some object or entity on the Internet. Depending on the specific mechanisms used, a UUID is either guaranteed to be different or is, at least, extremely likely to be different from any other UUID generated until 3400 A.D. The UUID relies upon a combination of components to ensure uniqueness. A guaranteed UUID contains a reference to the network address of the host that generated the UUID, a timestamp (a record of the precise time of a transaction), and a randomly generated component. Because the network address identifies a unique computer, and the timestamp is unique for each UUID generated from a particular host, those two components should sufficiently ensure uniqueness. However, the randomly generated element of the UUID is added as a protection against any unforseeable problem.
A UUID is specified as part of the tModel data structure, which represents a service type (a generic representation of a registered service) in the UDDI (Universal Description, Discovery, and Integration) registry. This mechanism is used to discover Web services.
UUIDs could be generated to refer to almost anything imaginable. Microsoft and some other software companies refer to GUIDs (global unique identifiers), a type of UUID used to refer to Component Object Module objects and other software components. The first UUIDs were created in the Network Computing System (NCS), and subsequently became a component of the Distributed Computing Environment (DCE) of the Open Software Foundation (OSF).