Re: The Path URN Specification

Michael Mealling (Michael.Mealling@oit.gatech.edu)
Tue, 21 Mar 1995 22:46:43 -0500 (EST)


From: Michael.Mealling@oit.gatech.edu (Michael Mealling)
Message-Id: <199503220347.WAA26944@oit.gatech.edu>
Subject: Re: The Path URN Specification
To: liberte@ncsa.uiuc.edu (Daniel LaLiberte)
Date: Tue, 21 Mar 1995 22:46:43 -0500 (EST)
Cc: uri@bunyip.com
In-Reply-To: <199503172258.QAA20216@void.ncsa.uiuc.edu> from "Daniel LaLiberte" at Mar 17, 95 04:58:25 pm

Daniel LaLiberte said this:
>     o If the TXT record is missing, then the URN does not resolve
>       into a server and the URN is assumed to be invalid. 

Some of my concerns with this approach are the same ones I have with Mitra's
approach. That concern is that by tying this so closely with DNS we are
excluding a very very large portion of our user base from becoming involved.
The power behind the web was that anyone could set one up without going 
through any official channels. I know that if I had needed to ask for
a TXT entry in our nameserver (which we don't do and probably won't do) in
order to put up a http server that we would just now be getting one setup.

In order for URNs to be used there must be no barriers to the system being
setup by anyone with an IP address. I would argue that scalability 
inherently depends on this or it will fail. I.e. URNs must be as easy to
setup and manage as URLs or folx won't use them. They often don't mind 
setting up additional software but DNS mucking is usually right out...

> To clarify the above algorithm, some examples are presented. The
> examples use the partial document tree specified previously. The DNS
> entries for this partial tree are: 
> 
>                               TXT           A
>              a.path.urn     -empty-       -none-
>           b1.a.path.urn    c2, port=n    ip-address
>        c2.b1.a.path.urn        port=n    ip-address
>           b2.a.path.urn   d.c, port=n    ip-address
>       d.c.b2.a.path.urn        port=n    ip-address

The concern I have here is that we are trading one kind of hot spot for
another. One of the problems we are trying to solve is the recurrence of
problems like that poor soul that setup the Shomaker-Levy-9 stuff. In this
case his machine may still not be that busy but the machine serving
those URNs is going to be slammed to the wall. We need to be able to
say that b1 resolves to multiple machines and that the resolution can
happen on multiple non-cooperating resolution servers. I realize this
can be done with caching of the DNS records but this function is not 
ubiquitously good enough among all the bind implementations out there.
I.E. I dont' think Microsoft's bind knock off will do it.

The last problem is almost anecdotal. I maintain my campus' nameserver.
It can serve the campus nameserver needs fairly well but if anything else
is loaded on it I fear for our nameserver. This isn't just us either....;-)

As far as using HTTP is concerned it really doesn't matter what you use
if all you are doing is URN lookup. What I would argue for is something
a little bit more powerful that can handle at least limited URCs instead
of just URNs. The possibilities of resource caching and replication become
much much more valuable. If you do want to distribute lookup of more than
just URNs then you need some form of query routing and at least a rudimentary
query language in your protocol. This could be added to HTTP or we could
use something like Z39.50 or whois++, I don't really care. Just as long
as it has 3 things:

1. query routing (preferably based on forward knowledge)
2. multiple query languages based on users needs
3. multiple data formats (i.e. MARC, TEI, whois++, HTML, etc).

The last two don't seem apparent until you realize that the library community
wants to play but they aren't about to scrap all of their MARC systems to 
play. The same goes for the HyTime folx, HyperG, etc. If the system can
dynamically map between these data formats and query languages then we
have something that we can use to  solve some current problems and some 
future ones with....

See you in Danvers!

-MM

-- 
------------------------------------------------------------------------------
<HR><A HREF="http://www.gatech.edu/michael.html">
<ADDRESS>Michael Mealling</ADDRESS>
<ADDRESS>michael.mealling@oit.gatech.edu</ADDRESS></A>