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URL Working Group                                       Charlie Kindel
INTERNET-DRAFT                                   Microsoft Corporation
<draft-kindel-uuid-uri-00.txt>   Expires 1 Year from November, 24 1997

                         The uuid: URI scheme


This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
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This memo describes a Universal Resource Identifier (URI) scheme that
allows resources to be uniquely named over time and space using
Universally Unique Identifiers (UUIDs). A UUID URI is a pure URI, in
that it contains no information about location. However due to the
uniqueness of UUIDs, a UUID URI is persistent over time, much like
URNs. UUID URIs are useful in situations where a unique identifier is
required that cannot or should not be tied to a particular physical
root namespace (such as a DNS name).

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INTERNET-DRAFT      <draft-kindel-uuid-uri-00.txt>      November, 1997


     1.   STATUS OF THIS MEMO....................1
     2.   ABSTRACT...............................1
     3.   TABLE OF CONTENTS......................2
     4.   INTRODUCTION...........................2
     5.   UUID URI...............................3
     6.   BNF FOR THE UUID URI...................3
     4.   SECURITY CONSIDERATIONS................3
     7.   REFERENCES.............................4
     8.   AUTHOR'S ADDRESSES.....................4
     9.   APPENDIX A - UUID URNS.................4
     10.  APPENDIX B - GENERATING UUIDS..........5


A UUID (also known as a GUID, for Globally Unique Identifier), is 128
bits long, and if generated correctly [UUID], is either guaranteed to
be different from all other UUIDs/GUIDs generated until 3400 A.D. or
extremely likely to be different (depending on the mechanism chosen).
UUIDs were originally used in the Network Computing System (NCS) [NCS]
and later in the Open Group's Distributed Computing Environment [CAE

One of the main reasons for using UUIDs is that no centralized
authority is required to administer them. As a result, generation on
demand can be completely automated, and they can be used for a wide
variety of purposes. UUID generation algorithms support very high
allocation rates: 10 million per second per machine if you need it, so
that they could even be used as transaction IDs. UUIDs have a fixed-
size (128-bits) which is reasonably small relative to other
alternatives. This fixed, relatively small size lends itself well to
sorting, ordering, and hashing of all sorts, storing in databases,
simple allocation, and ease of programming in general. The primary
disadvantage of UUIDs is that they are difficult for humans to parse.

Universal Resource Identifiers [URI1] based on UUIDs are useful in
situations where a unique identifier is required that cannot or should
not be tied to a particular physical namespace (such as a DNS name).
Many platforms have built-in UUID generators (any system with DCE or
COM support, for example). However, for those that do not the source
code to the reference implementation UUID generator has been made
available as part of the Leach and Salz Internet-Draft [UUID].

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INTERNET-DRAFT      <draft-kindel-uuid-uri-00.txt>      November, 1997


As mentioned above, a UUID is a 128 bit value. UUIDs can be expressed
in either binary or string form. Because URIs are expressed as string,
this memo is only concerned with the string representation. A typical
UUID in string form looks like this:


To enable the use of UUIDs as URI's within Internet documents this
memo defines a simple UUID URI scheme. Using the scheme described in
this memo, the above UUID would be represented as:


The basic structure of a UUID URI is:


where <uuid> is a string representation of a UUID, which is documented
in [UUID]. The optional set of qualifiers are specified as name/value
pairs separated by semi-colons. There are currently no qualifiers
defined. However, UUID URI parsers should be written to gracefully
ignore any characters that appear after the last character of the UUID
(UUID strings are always 36 characters long).
UUIDs must be generated using well known algorithms.


A uuid URI begins with the scheme prefix "uuid" and is defined by the
following grammar:

     uuid-uri       = "uuid:" uuid [qualifiers]
     uuid           = 8hex "-" 4hex "-" 4hex "-" 4hex "-" 12hex
     qualifiers     = [";" name = value]*
     hex            = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" |
                    "8" | "9" | "a" | "b" | "c" | "d" | "e" | "f" |
                    "A" | "B" | "C" | "D" | "E" | "F"

The set of qualifiers and their BNF syntax are currently not defined.


It should not be assumed that UUIDs are hard to guess; they should not
be used as capabilities.

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INTERNET-DRAFT      <draft-kindel-uuid-uri-00.txt>      November, 1997


[UUID]    P. Leach, R. Salz, 'UUIDs and GUIDs', Internet-Draft,
          00.txt>, February 24, 1997.
[CAE RPC] CAE Specification, 'X/Open DCE: Remote Procedure Call',
          X/Open Company Limited, Reading, Berkshire, UK
          (xopen.co.uk), 1994. X/Open Document Number C309. ISBN 1-
[NCA]     Lisa Zahn, et. al., 'Network Computing Architecture',
          Prentice Hall, Englewood Cliffs, NJ, 1990
[MD5]     R. Rivest, RFC 1321, "The MD5 Message-Digest Algorithm",
[URI1]    T. Berners-Lee, R. Fielding, L. Masinter, "Uniform Resource
          Identifiers (URI): Generic Syntax and Semantics", 05 Nov
          1997. <http://www.ics.uci.edu/pub/ietf/uri/draft-fielding-
[URI2]    T. Berners-Lee. "Universal Resource Identifiers in WWW: A
          Unifying Syntax for the Expression of Names and Addresses of
          Objects on the Network as used in the World-Wide Web." RFC
          1630, CERN, June 1994.
[URL]     T. Berners-Lee, L. Masinter, and M. McCahill. "Uniform
          Resource Locators (URL)." RFC 1738, CERN, Xerox PARC,
          University of Minnesota, December 1994.

Charlie Kindel      One Microsoft Way Redmond, WA 98052-6399, U.S.A.
                    Fax: +1 (206) 936 7329 Email:


Universal Resource Names (URNs) have great promise. However they are
not widely implemented at the time of this writing, and it is not
clear when implementation will become widespread. However, it is
likely that UUIDs will also be useful in some situations where URNs
are used. For this reason, this appendix proposes a UUID URN scheme.
The syntax is exactly the same as the UUID URI scheme described above
with the exception that the uuid: scheme qualifier be preceded with
the urn: qualifier. For example, a UUID URN would look like this:


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Any system that includes a DCE RPC runtime will provide built-in UUID
generation facilities. At the lowest level these facilities are
exposed through the RPC library API "uuid_create()".

On Windows systems, there are two equivalent APIs for generating
UUIDs. One is exposed by the MS RPC library (UuidCreate()), and the
other via the Component Object Model (COM) library (CoCreateGuid()).
CoCreateGuid() is simply a wrapper around UuidCreate().

On systems with an RPC runtime, a command line utility named "uuidgen"
is provided. On the Windows platform, this tool is available as part
of the Win32 Software Development Kit and supports the following
command line syntax:

     usage: uuidgen [-isonvh?]
     i - Output UUID in an IDL interface template
     s - Output UUID as an initialized C struct
     o<filename> - redirect output to a file, specified immediately
     after o
     n<number> - Number of UUIDs to generate, specified immediately
     after n
     v - display version information about uuidgen
     h,? - Display command option summary

The command line syntax may vary from system to system.

                Expires 1 Year from November, 24 1997

Kindel                                                          page 5

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