Re: Persistent Documents and Locations
Mon, 21 Aug 95 15:41:41 -0400

Message-Id: <>
To: "Karen R. Sollins" <>
Subject: Re: Persistent Documents and Locations 
In-Reply-To: Your message of "Mon, 21 Aug 95 11:21:18 EDT."
Date: Mon, 21 Aug 95 15:41:41 -0400

>people who built capability systems many years ago in much more
>limited contexts realized that revocation had to be an integral part
>of any naming/access system.

This why cache schemes need timeouts, so that people don't
believe forever the information they've gathered.  So, how
long should a URL be valid for?  One could carry individual
timeout information with each URL (like DNS can), or one
could set a Web-wide value, such as a week, beyond which one
would not believe that URL any longer.  So, no matter when
one received the URL, one could not depend on it for more
than that week.  After that, one would need to verify the
URL by going back to the longer-lived URN (?) and retrieving
the associated URL(s) again.  Perhaps URNs should have a
life of a year, after which they should be questioned as to
their validity.  

One problem:  who validates URNs, since they are the 
longest-lived element in the UR* universe?  Like DNS,
one can find out that a URN is no longer valid.  The issue
then is to find out a source from which one can get the new
form of the URN or an alternate URN or confirmation that the
URN doesn't exist at all anymore.  This is usually an offline
task (like calling a friend to learn what the real domain
name is).