W3C home > Mailing lists > Public > www-archive@w3.org > March 2009

stuff goes away

From: Larry Masinter <masinter@adobe.com>
Date: Sun, 15 Mar 2009 18:45:37 -0700
To: Jonathan Rees <jar@creativecommons.org>
CC: "www-archive@w3.org" <www-archive@w3.org>
Message-ID: <8B62A039C620904E92F1233570534C9B0118CD2A0EC4@nambx04.corp.adobe.com>
I'm still stuck on the lifetimes of URIs vs. lifetimes
of statements, in engineering the semantic web:


"... you might be able to
make some plausible predictions or credible commitments.."

Stuff goes away. Mean time between site failure might be less
than 10 years. Companies change their names, merge, split,
go out of business, stop doing the business that caused them
to bring up the web site. Students graduate. Non-profit
organizations change brands. Web technology itself is
only 20 years old, 20 years from now. Sure, maybe some will
still be around, but on the average, no one has the
foundation or insurance policy to guarantee that a
URI will still be around to respond "200-" to anything
for the expected lifetime of the assertion being made.

Many industries and applications have a requirement that
the statements made and inferences about them need to last
much longer than 20 years: government documents, descriptions
of building plans, life insurance policies.

Anyone who wants to make a "semantic web" statement which
need to have meaning beyond the guaranteed lifetime of the
web sites used to form their "ontology" cannot link the
meaning of those statements to the future 200-response
expectation of the referenced web site. The expected
lifetime of any particular piece of web content is much
less than the needed lifetime of the validity of semantics
and understanding of semantic intent.

I think it is more natural to assume that there are
*no* stable URIs in the long run: every URI has a
lifetime, we wish every one to have as long a life
as possible, but every single URI will, at some point
in the future, evaporate. Consider:

at any instant, there are:
* People who want to make semantic web assertions P
* assertions that those people want to make 
   A(p) for p in P
* for each assertion, their desired lifetime
  (how long each person wants to make sure the
  assertion is interpretable)    
    D(a) for a in A(p) for p in P
* terms needed in those assertions
    T(a) for a in A(p) for p in P
* URIs under the control of those people 
  which are appropriate 
    U(t) for t in T(a) for a in A(p) for p in P
* expected lifetime of those URIs
    E(u) for u in U(t) for t in T(a) for
   a in A(p) for p in P.


Most people don't have the ability to make
assertions for which the URIs they use have
an expected lifetime longer than the desired
lifetime of all of the assertions they want
to make.

for large percentage of p in P
there are some assertions a in A(p)
such that for some needed term
t in T(a), such that the desired
lifetime of the asertion D(a) exceeds
the maximum expected lifetime of
all resources available to p.


Received on Monday, 16 March 2009 01:46:23 UTC

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