Date: Mon, 26 Sep 94 16:19:35 CDT
From: liberte@ncsa.uiuc.edu (Daniel LaLiberte)
Message-Id: <9409262119.AA17585@void.ncsa.uiuc.edu>
To: uri@bunyip.com
Subject: Re: AGENDA ITEMS for December IETF meeting
Regarding URN resolution, there are a number of specific issues to
discuss, and other people should at least raise other issues now. I'd
like to discuss scalability a bit now because I'd like to be convinced
that there is a solution out there waiting to be discovered/invented.
The issue of URN scalability should be divided into two separate
issues: the scalability of name assignment and of name resolution.
Assignment of trillions of names is not really very difficult given
even a modest subdivision of the name space.
The real problem comes in the resolution of URNs to URCs (and then to
URLs) since that happens many times for each document after it has been
created. (Of slightly lesser concern is the scalability of URC
updates, though for some kinds of documents, there may be many more
updates than accesses.) Therefore, the scalability requirements for
URNs must be geared toward solving the name resolution problem, not
the name assignment problem.
To be scalable, I believe the name space must be hierarchically
structured. Whether the hierarchy is at the level of naming authories
or within each naming authority (as a prefix to the opaque string)
makes no difference as long as it is a standard, public hierarchical
scheme. That is, it is not sufficient for the hierarchy to be hidden
within opaque strings, known only to name resolvers. The reason for
this standard, public hierarchical scheme is so that resolution of
URNs may be delegated to resolvers that either know how to resolve a
particular URN or know where to delegate the resolution, and
furthermore so that clients may also know which resolver to go to
directly, or which one is close if a direct one is not known.
For the same reasons that DNS cannot be a flat name space, URNs cannot
be a flat name space. The URN resolution problem is several orders
of magnitude more difficult than domain name resolution.
In IETF documents, I've seen references to the *possible* need for a
hierachical name space, but I believe scalability *requires* it, or at
least, I haven't seen any argument to the contrary.
Daniel LaLiberte
National Center for Supercomputing Applications
liberte@ncsa.uiuc.edu