Date: Thu, 21 Oct 93 14:21:01 +0100
From: Tim Berners-Lee <timbl@www3.cern.ch>
Message-Id: <9310211321.AA05697@www3.cern.ch>
To: eostrom@gac.edu (Erik Ostrom)
Subject: UR* terms
Eric,
You are right, the
<http://info.cern.ch/hypertext/WWW/Addressing/Addressing.html>
document was not very explicit. The intention was (as
it now reads) "WWW will use any new forms of naming which give
features such as persistence and redundancy, when the are available,
by extension of the set of schemes in the URI.
(I don't think the URL: was ever intended as wrapper, but as a
prefix. As John Curran says.)
I have a added a list of terms appended.
Repetiton-- if you agree, skip! :-) : My point is that
those who think that the difference betwen URLs and URNs
is NOT fundemental.
We all agree we need some
better naming than what we have, but I'd be reluctant to introduce
a prefix which basically means "pre-1993".
Just look at Mitra's point that the news: scheme ought not
to be a URL, ought to be a URN.
I resist putting all existing schemes of URIs
into a subset before we have an examples of schemes which
are not in that subset. So I want to play down this
difference between URLs and URNs. URCs are a diffeent
matter, different animal, different syntax.
Tim
___________________________________________________________
UR Terms
URI Uniform Resource Idenifier. (originally,
Universal). The generic set of all
names/addresses which are short strings
which refer to objects. The exact
properties of each URI scheme depend on the
scheme you are talking about. (Originally
UDI in some www documents).
URL Uniform Resource Locators. Term introducted
by the IETF in forming the URI working group
to point out that currently available URIs
are mainly addresses rather than names.
Exactly what consitutes a locator as opposed
to a name is basically lack of persistence,
but this is a much discussed point and
impossible to define precisely. In
practice, the set of schmes referring to
existing protocolls, listed in the URL
specification[16].
URN Uniform Resource Name. 1. Any URI which is
not a URL. 2. A particular scheme which is
currently (1991,2,3) under development by
the IETF, which should provide for the
resolution using internet protocols of names
which have a greater persistence than that
currently assiated with internet host names
or organizations. When defined, a URN(1)
will be an example of a URN(1).
URC Uniform Resource Citation. A set of
attribute/value pairs describing an object.
Some of the values may be URIs of various
kinds. Others may include, for example,
athorship, publisher, datatype, date,
copyright status and shoe size. Not
normally discussed as a short string, but a
set of fields and values with some defined
free formatting.
URM Something introduced by Michael Mealing
along the lines of a URC encoded into a
string, with a rather peculair syntax. ;-)
___________________________
I might even put in my previous diagram
_______________________________________________________
| |
| _______________ _______________ |
| | ftp: | | urn: | |
| | gopher: | | fpi: ? | |
| | http: | | | |
| | etc | | | |
| |_______________| |_______________| |
| URLs URNs |
|_______________________________________________________|
URIs
Venn digram. URI is the universal set by definition. The
next most important entity is the namspace identified by
its prefix. The groupings "URL", "URN" are useful for discussion
but are not fundamental. It is difficult to generalize about
groupings for urns and urcs etc when they don't exist, so we
talk about the class of URNs and the new urn: protocol as one.
Why not? The last thing we need is more names. And maybe
the urn: space will be all that is needed for the URN function.