URI WG minutes

Larry Masinter (masinter@parc.xerox.com)
Thu, 20 Apr 1995 18:18:21 PDT

To: minutes@CNRI.Reston.VA.US
Cc: uri@bunyip.com
Subject: URI WG minutes
From: Larry Masinter <masinter@parc.xerox.com>
Message-Id: <95Apr20.181834pdt.2761@golden.parc.xerox.com>
Date: Thu, 20 Apr 1995 18:18:21 PDT

Minutes of Uniform Resources Identifiers Working Group, April 3 & 4,
1995.  Thanks to Margaret St. Pierre, Stu Weibel for taking notes in
Session 1 and 2, and Karen Sollins for contributing notes. I have
edited the minutes to merge the notes from the various contributors,
and hope that I've not done too much violence to the sense. Please
send corrections, additions, and flames.


Session I  

* Review of agenda, accept minutes from last meeting.

* Leslie Daigle presented URAs (Uniform Resource Agents). 
URAs are a means of specifying network activities.  For more information on
URAs, see draft-ietf-uri-ura-00.txt.

Briefly, URAs are a means of expressing complex Internet activities.
The goal is to capture an object with 5 parts:

	1. identification and URC
	2. data elements required
	3. internet resources required
	4. definition of find: how does one access things.  Scripting
	5. postprocessing mechanism on results for client of URA.

* A 10-minute presentation was given to summarize each of the URN
schemes given below.  For more information on each scheme, see the
associated URL.

* Ron Daniel presented the Schema/Authority/Element URN scheme. 
Key features
  - Syntax is same as Mitra's, e.g., <URN: Schemeid: Authorityid:Elementid>
  - Each name determines the character set restrictions for following field.
  - It uses 'DNS' for SchemeID, then a FQDN for AuthorityID.

* Michael Shapiro presented the Path URN scheme.
  Key features:
  - A uniformly hierarchical namespace, dymanically reconfigurable, etc.
  - Totally separate from hostnames, but have to emulate what DNS 
    is doing now.  In prccess of walking down the path learns about where a
    server is.
  - The client chooses the lowest level server; everything below that served 
     by that server

   How is the Path scheme different?
   + Just one of many naming schemes - each with different semantics
   + Hierarchical vs flat
   + Dynamically configurable - servers can move independent of names
   + Implemented on top of existing DNS and HTTP

   Does the Path scheme meet the URN Requirements?
   + Global scope - yes
     Root is known to all clients
     Each node will have a corresponding resolution service
   + Global uniqueness - yes
   + Persistence - as much as any scheme could be
     Names live forever
     Naming authorities can disappear
     Path naming authorities/resolvers are responsible for their children
   + Scalability - yes
     Assignment is hierarchically distributed
     Resolution is hierarchically distributed
   + Legacy Support - sort of
   + Extensibility - sort of
     Use Generic URL syntax for other URN schemes
   + Independence - yes
     Name authority only constrained by the syntax and	encoding rules
   + Resolution - yes
     Path->URL, or Path->URC, or Path->object, all permitted (by HTTP)
     Scalable resolution because it is publicly hierarchical

   Frequently Asked Questions
   + Are we using existing DNS hostnames? - no
   + How will this impact DNS?
      Load on local and remote nameservers and caches.
        nameservers - O(1) hit per node
        caches - larger (due to TXT and more  activity)- unknown. needs study.
         a few new rules
	 initially more work, but not much after that
   + What happens when a Path naming authority or resolver goes out of business?
     The parent is responsible to take over or redelegate.
  In the discussion, some controversies arose about the use of DNS or
  the recreation of name resolution services. There was also a
  question about whether the correct algorithm is to walk up the 
  tree or down; they think that top-down walking will allow them
  to take advantage of caching.

* Bill Arms presented the Handle service. This is described in
<URL:http://www.cnri.reston.va.us/home/cstr.html>.  This effort is
happening independently of the IETF; it comes from the CNRI global
digital library. It is a pure naming system; no URC or
meta-information is returned. The syntax very similar to other
schemes: naming_authority/string (where string can be flat or
hierarchical).  Any naming authority can name subauthorities.  A
global authority provides global naming.  For resolution it makes no
use of any structure in handle; they intend to have global and local
resolution and caching.  When you send a handle to a handle server,
you get back everything stored with it.

They are building handle server mechanism with global servers and
caching, and talking with NCSA about embedding the resolution
mechanism in web clients. Use hash to map to a global server.

Discussion brought up a question of aging; what happens when the cache
is out of date? This is more of a problem for local servers.

* Keith Moore gave a quick refresher about LIFNs, used to name a
particular version of a file. They expect that location and file
servers not co-located.  Can have a small number of location servers
and LOTS of file servers.  It omfortably deals with file server or
communication failures, because all locations have mirrors of files.
* Mitra and Michael Mealling and Chris Weider spoke about the "General" syntax.

It is fast, implementable & based on current technology. They want to
be "THE" scheme, because we need a single mechanism, that it is
trivial to implement in clients, or, by using proxies, client builders
don't need to do anything.  The important design goal was the need to
do de-resolution in around 1 sec.

4. The remainder of Session 1 was devoted to discussion of the
presentations, with a chance to ask any of the presenters questions on
their proposed URN schemes.  The following issues were raised, and a
number of (sometimes contradictory) points were raised on each of
these issues, as described below:

Issue: Should one protocol or multiple protocols be used (e.g.,
whois++ and http ) ?

- A single protocol approach would make it possible for client
  software not to have to change to support all protocols.

- A single protocol would permit wider adoption.

- A security model that would support multiple protocols may be
  difficult to achieve, although may not be a problem with a
  security scheme such as SSL.

Issue: Will the URN schemes be able to scale up to over one million
publishers on the net, and how will administration of such a large
number of URNs be handled?

Each scheme scales in terms of name definition, but persistence of
name management.  What does one do for resolution of names for naming
authorities that have gone out of business.  Problem of scale is
resolution.  Handle scheme - there is a problem of global updates, but
need to register authorities, not actually objects.

- Scaling: name assignment separated from name resolution - different

- A global server may have problems updating if the number of URNs
  doubles each year.

- The solution to this problem depends on how many URNs are 
  registered globally versus locally.

- URNs have to be globally resolvable.

- Locality of reference cannot be assumed on the Web, e.g., in Norway,
  most references are to local organizations or to the US.

- The URI group should look into making use of the work the DNS group
  is doing to handle administration and namespace issues.  DNS won't
  scale.  If make barrier to users that can't define names without
  going to DNS administrator, don't do this without talking with DNS
  folks about revising to do much greater scaling.

- Use DNS name as the registration authority, e.g. the resolver 
  for gatech would be "uri.gatech.edu".

- Not all URLs will have a corresponding URN. There are not going
  to be that many "published" documents that need to be cataloged
  for the long term, and thus the number of URN's assigned will not
  be a major problem.

- The URN scheme should be built to handle the assumption that
  everyone will want to author, and that publishers should ensure
  that URNs stay around for the long term.

- Name assignment is separate from the name resolution scheme, and
  should be solved separately.

- People would be willing to wait for name resolution.

- People would not be willing to wait for name resolution; name
  resolution should occur with less than a one-second retrieval

Issue: How is payment for these schemes handled?

- A hierarchical URN scheme is attractive because billing can be
  done locally.
- Sometimes archivers will pay, while in some cases people will pay
  for their own. 
- For the present for DNS, if pay for DNS naming then pay and 
  otherwise not.

* Question: are LIFNs dependent on using something that will never
hash to same id?  Keith: no, you can use any form of hash function.
Security comes from file servers, not names.

*Peter D.: one protocol vs. many protocols? Many folks responded
saying that we'll need to deal with more than one, but shoot for one
for now.  The key thing is that clients may only have a single hook.
Using a proxy scheme may solve the problem.  Mitra urged that need a
single scheme and protocol or will lose.  We're really just talking
about interface definition.  Keith claimed we need to define a single
protocol on the wire.  From floor: should be using proxy servers that
can speak multiple protocols.  Security questions: will one be willing
to run resolutions at firewalls?


Session II, 1300-1500

1. Relative URLs: Roy Fielding

The draft was declared complete without objections, and will be
submitted to IESG for 'last call' before becoming standards track RFC.

2. Z39.50 URL Status Report John Kunze

The ZIG mailing list has raised enough questions on this that the
author isn't ready to propose adoption.  The URI list is asked for any
comments on the draft, however.

3. Relative URL draft
  Roy Fielding (relative URLs): no more comments.  Done unless anyone 
  has anything to say will go to last call.

4. Finger, Mailserver URL-scheme extension mechanism


   No comments on either... both will be submitted for last call
   and move to standards track.

   ISSUE: How will such extensions be vetted in the future?

   The working group is now reviewing extensions (3 so far)... in
   future months, someone must edit revision of URL draft, and decide
   how extensions will be done in future.
   No one present at the meeting volunteered to adopt these responsibilities,
   though there was recognition that it is necessary and important.

   Need stronger mechanism than saying that IANA will do it.  Can we 
   use the MIB mechanism?  Mime type people also do this.  For MIBs 
   all work goes through WG.  For mime types, work is done by posting 
   and discussing on a mailing list.  Need to set up process for when WG 
   no longer exists.  Suggestion of an intelligent assistant editor for 
   IANA.  Will need someone in next few months to revise URL 

5. URC Scenarios and Requirements Ron Daniel and M Mealling

The authors are seeking feedback concerning the minor modifications made
to the document (Daniels, Mealling). We deferred discussion on this
issue in order to get back to the URN discussion.

The syntax discussion was shut down last time, in order to
implementation.  Currently, always want to support multiple query 
languages.  By next time would like to running code and revisions of
document.  Hope to have it close to last call next time.

Ron: Want to make sure that people understand that there isn't just
one URC.  There may be one default one.  No required attributes.  
There is a question of whether a single data model or more than one.

6. The remainder of the session was given over to continued discussion
of the 5 URL schemes and associated issues.

The following assertions or comments reflect the sense of the discussion:

* It is time for a new namespace/resolution system - the existing DNS is
fragile and flawed; extending these flaws into the URN arena will
propagate these flaws (eg.: flatness of .com space)

* URNs will not, of themselves, solve the problem of persistence of
OBJECTs... only persistence of names.  Schemes need not *assure*
persistence of objects, but some thought should be given to assure
that the problem is not exacerbated by the scheme.

* Most of the URN schemes don't really go into details about what
happens when something moves.  So far have dealt only with what
happens when a whole organization moves.  Granularity of mobility must
be addressed. For example:
- All web documents from CERN move to INRIA, but high-energy physics
  documents stay at CERN. What happens to URNs for the web documents?

- A grad-student graduates but someone wants to retain editorial
  control of one of his pages. How can this happen?

- A university retains all articles by staff members; someone on the
  staff publishes the exact document in an online journal.  Does it
  get a new URN, or just keep the old one?

* We have two different requirements: (1) URNs resolvable quickly (2)
URNs should last a long time. However, we don't have a requirement
that URNs should be resolvable quickly for the forseeable future.
That is, over time, as the number of resources grow and items migrate
from one location to another, we don't have to design for efficient
access in the future.

* DNS doesn't guarantee uniqueness in time; however, it is possible to
add some limited time stamp (e.g., DNS name plus year, or DNS name
plus year and month.) This gives uniqueness over time without adding a
full 32-bit timestamp. In general, qualification of a name space with
time stamp (possibly low resolution; year or year-month) will help
make the inclusion of human readable info in URNs more accessible to
long term interpretation.

* Claim: we should always go to URC in order to find URL.  It should
be possible to modify set of URLs in a URC. There is an issue of
finding all copies of the URC - this is tied to publisher being
responsible for default URC for all time.

* Proposal: in near term, the agent that handed out the name will do
resolution, but we quickly will need an alternate solution.  This
suggests that all moves are handled based on naming authority or sub

* We should identify solutions to DNS problems and take advantage of
the existing investment in technology and administrative
infrastructure...  do not confuse architecture (sound) with
implementation (currently weak).  Join the DNS WG if you think you can
invent a better namespace; anyone who thinks this can be done probably
doesn't understand the problems.

* One or several URN schemes?  There may be call for several, some
tailored to specific aspects of the problem set.  eg: LIFNs do not
solve all the problems of the URN domain, but might be very useful as
a guarantee of version identity (imagine wanting to assure a JAVA
applet version or identity).

* Name Resolution: Should it be to a location (URL) or to a URC?

* There is a need for a private part of the name space; (spook.gov,
snidely.com, privacy.edu, for eg., will need mechanisms for assuring
* Are we trying to solve NIDR with permanent names?  Names should last
as long as the issuing agency...  go to a permanent naming authority
if you want your stuff to last.
* Names with human-readable components (built in semantics) are
intrinsically less persistent than those made of opaque strings (OIDs,
ISBNs, etc.)
* Schemes must be maintainable over time frames of hundreds of years
to achieve acceptance as identifiers of important cultural records by
research libraries.

* Some assert that semantics should be kept out of the name space
mechanism.  Others assert that semantics may be included, but only as
convenience; they should be ignorable (processable as content free
tokens). Hierarchical resolution cannot be done with acceptable
resolution times (sub-second responses). Overloading names with
semantics is necessary to achieve low resolution times

* Some assert that it's time to decide on a syntax and character set
so experimental work can go forward. On the other hand, we must agree
on the semantics before we do a syntax.

* A URN Scheme Bake Off is proposed for the Stockholm (or failing
that, the Dallas IETF).
 Set ground rules by 20th of April 
 Report preliminary results by Stockholm
 Argue results in Dallas
Preliminary ground-rules:
   Use URL requirements and syntax for URNs (e.g., no spaces),

   Invent new URL-'scheme' to describe your URNs, but don't use 'urn:'.

   Explain how scheme meets URN requirements.

   Describe behavior and performance in the use scenarios, especially
   when resources have moved.

Chris Weider, Larry Masinter, and Tim Berners-Lee are nominated to
establish ground rules (having spoken up about them in the meeting),
though comment and proposals from others are welcome.
Theoretical models of performance, though suspect, may also help 
to shed light or point in the direction of further experimentation.