# Re: Why URN is a subset of URL

Peter Deutsch (peterd@bunyip.com)
Thu, 6 Oct 1994 20:22:49 -0400

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    Message-Id: <9410070022.AA10974@expresso.bunyip.com>

    From: Peter Deutsch <peterd@bunyip.com>

    Date: Thu, 6 Oct 1994 20:22:49 -0400

    In-Reply-To: "Daniel W. Connolly"'s message as of Oct  6, 10:40

    To: "Daniel W. Connolly" <connolly@hal.com>

    Subject: Re: Why URN is a subset of URL

[ Daniel W. Connolly wrote: ]

> In message <9410061333.AA09997@expresso.bunyip.com>, Peter Deutsch writes:
> >
> >> URLs are resource _locators_; URNs are _location_ independent names. How
> >> something which is location independent can be a member of a subset of a
> >> set of locators is a little beyond me at the moment.
> >
> >Ditto.
>
> How about a venn diagram?

<[* cute ASCII art image deleted *]>

I seem to have lost a bit of the context, so I can't recall
what an "fpi" is, but this diagram does seem to summarize
the output of the acronym wars. The issue is whether every
participant in this thread agrees on the need for the two
classes shown. I thought I was hearing that they didn't.

In particular, I was agreeing with the statement by someone
(sorry, the attribution's been lost) that there was a
difference between locators and names. In the diagram, I
would map the first to URLs and the second to URNs. Thus,
one is not a subclass of the other, both are subclasses of
the superclass URI. Others have claimed that URNs are a
subclass of URLs.

> > For those who claim they don't need these, no
> >sweat.
>
> I have seen noone claim that we don't need the features
> of replication and authentication.

I didn't say anyone did. I was agreeing with a statement
about URNs not being a subclass of URLs.

As an aside, I have a bit of a problem with using your two
terms in this context, as they carry other connotations in
the computer field (I don't disagree with the concepts
that you claimed they encapsulate, I just tend to react to
the terms in a different way they you might intend, which
can lead to confusion). Now that I understand what you're
saying I can live with it, but I'll continue to use my
terminology so I can keep my thoughts clear in my mind.
Please bear with me.
Now, to return to your last sentence. Actually, you
dropped the context of what I was responding to. What was
written was:
# > URLs are resource _locators_; URNs are _location_ independent names. How
# > something which is location independent can be a member of a subset of a
# > set of locators is a little beyond me at the moment.
#
# Ditto. For those who claim they don't need these, no
# sweat. . .

Thus, I agree with you that we don't think _anyone_ is
questioning the need for replication or authentication (as
you use these terms). I was merely agreeing with a
different statement - that it was hard to see how URNs
could be a subset of URLs. If you endorse Tim's Venn
diagram, presumably you agree with us on this, since what
the diagram shows is that they are two separate classes of
the superclass URI.

I certainly don't mind if others believe that such a
subclass relationship exists, but I disagree with the
belief and am working on the assumption that the
difference is real and measurable. Others should
understand this if they are to understand my postings
(assuming you've even read this far! :-)

> > I certainly see a need and we plan to deploy them
> >soon.
>
> I agree. I just think that any plan that is incompatible with
> the WWW addressing syntax is a waste of valuable resources.

A couple of points here. It is my understanding that what
comes out of the URI working group is not supposed to be
"the WWW addressing syntax", but the "IETF addressing
syntax". We of course want it to be as compatible as
possible with previous versions of WWW, but we must also
accomodate the sometimes conflicting needs of other
developer communities, including gopher, WAIS, Prospero,
etc. Thus, there was never a guarantee that there wont
be some changes needed to later versions of WWW if the WWW
developer community were to adopt the IETF standard along
with the rest of us. After all, we required accomodation
from the other developer communities, too.

I apologize if you meant to say "IETF addressing syntax".
It's just that in a multiple disciplinary group such as
this omitting such distinctions can sometimes affect the
task of consensus building. Please don't take offense if
I'm working this too hard.

Next, I would reply that forcing the world to adopt all of
the WWW URL syntax without modification at this point is
more that a waste of valuable resources. It's plain wrong.
I can enumerate areas where this would cause problems for
others and thus is not necessarily the right thing to do.

As but one example, I see problems if the WWW community
were to insist on the need for partial references in the
core standard, as to me they only make sense in the
context of a single homogenous system, such as WWW. I have
no trouble with WWW using them internally, I just don't
think they have a place in the current URL standard, given
where the rest of the community is right now and what we
expect people to be doing with these things. Either the
WWW community should document an extension (which I gather
is the current plan in moving them to an appendix or
whatever) or simply build their own URLs on IETF URLs, as
I understand you can build extensions to a DTD provided
you don't change the core DTD.

Having said all this, I'll agree that we don't want to
indulge in gratuitous changes that break things for the
sake of change. Still, if URNs _are_ something different
from URLs (which some claim they are not, which I believe
they are) then there should be no problem with examining
possible changes to the syntax. After all, that's what
we're here for.

Recall that we didn't insist that DNS domain names only
consist of digits and periods, just because that's how IP
addresses are represented. We use those two items
differently, and this is reflected in their syntax. They're
complementary, but processing them requires some different
code and being able to detect the difference
algorithmically is a win.

I feel the same way about URNs and URLs, although not
everyone on this list seems to agree. I repeat my last
remark - that's no sweat. Future info services from
Bunyip will serve URLs (soon I hope) and URNs as well.
Given the spectacularly slow progress on defining URNs, I
suspect we're going to simply deploy a strawman syntax
pretty soon, but I offer my personal assurances to this
list that if and when we see a consensus (in the form of a
suitable RFC and so on) we'll support whatever this group
endorses. Meanwhile, there's a net to build and I plan to
push the developers to put something out on this "soon".

- peterd

    --
    ==============================================================================
    ...
    "It's a -. Shall I tell him?" he asked, looking at Bill. Bill nodded, and
     the Penguin leaned across to Bunyip Bluegum and said in a low voice,
     "It's a Magic Puddin'."
    ...
    "that's where the Magic comes in," explained Bill. "The more you eat the more
     you gets. Cut-an'-come-again is his name, an' cut, an' come again, is his
     nature. Me and Sam has been eating away at this Puddin' for years, and
     there's not a mark on him."
                                   "The Magic Pudding", by Norman Lindsay

           Sounds like a pretty good analogy for the Internet to me
              (and yes, that's where we got the name "Bunyip"...)
    ==============================================================================

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