W3C home > Mailing lists > Public > www-tag@w3.org > July 2003

Re: resources and URIs

From: Graham Klyne <gk@ninebynine.org>
Date: Tue, 22 Jul 2003 10:27:03 +0100
Message-Id: <>
To: Tim Berners-Lee <timbl@w3.org>
Cc: pat hayes <phayes@ihmc.us>, www-tag@w3.org


Thus far, I believe we are in complete agreement.  I think the question 
that remains is then how to present all this in a web architecture document 
in such a way that:
(a) corresponds to the informal notions that we as people (users, 
engineers, programmers, etc.) have about identity of things and concepts in 
the real world (and beyond), particularly in the notion of a URI as "global 
identifier",  and
(b) is not in conflict with the notions of interpretation and denotation 
that underpin the model theoretic semantics that have been adopted to give 
formal expression to some aspects of web architecture.

This is where I thought that Dan's description of identity could help, 
because in this view it is clear that identity != denotation (or 
interpretation).  Pat has said on occasion (if threads "nearby" this, if 
not this thread) that he doesn't know what we mean by "identity" when we 
talk about URIs.  We agree that we, as people, try to use a URI to refer to 
a "single", more or less consistent, concept that is a topic of 
communication.  But there is no way to formalize this single concept:  I 
think the best we can do is to describe it as a kind of "locus" of 
denotations from interpretations that satisfy some formal statements we can 
make about it.

There may also be other things that we say about these concepts that cannot 
be formalized, except to the extent that we, as people, are broadly 
prepared to accept (as valid? useful?) the results of certain computations 
performed upon them according to well-defined rules (programs).  This, I 
think, is pretty much how the present "informal" web works today, and such 
an element will always be present in our use of it.  But until we can 
remove criteria like "people are broadly prepared to accept", such 
statements are beyond the reach of our formal systems.

I think this is all consistent with your own ideas about evolvability in 
the "designissues" series, penned some time ago (sorry, I'm offline and 
can't grab the URI).  We tried, and failed, to capture some of this with 
the so called "social meaning" elements of RDF.  Finding a way to describe 
these ideas that is acceptable to a broad range of people is very 
difficult.  I sense we need to try, in particular being clear about those 
things we cannot specify, if the semantic web is to develop as a seamless 
extension of the current web.


At 08:41 21/07/03 -0400, Tim Berners-Lee wrote:

>On Sunday, Jul 20, 2003, at 03:26 US/Eastern, Graham Klyne wrote:
>>Your message below seems closer to my understanding, except your comment 
>>about "assumption of a single interpretation" -- maybe this is just a 
>>terminological slip, but if we're talking about interpretations in a 
>>model theoretic sense, I think it's important to not try and claim any 
>>*single* interpretation.
>I'm not claiming that there is any single *well defined* interpretation.
>What I do, as you do, is point out that under certain rules, the 
>deductions (and action)  your agent makes are indistinguishable from those 
>of an agent who does assume a single interpretation.
>>[Background terminology check:  An "interpretation" arbitrarily assigns a 
>>single value from some domain to each of a set of names.  A "denotation" 
>>of a name is the value assigned to that name by some given 
>>interpretation.  Thus, for a given name there are multiple denotations 
>>corresponding to each interpretation that mentions the name.]
>Absolutely. ("arbitrarily"?.  An agent considers interpretations which are 
>consistent with the data.
>So when I see and chose to believe
>   <#pat> contact:mailbox <mailto:phayes@ihmc.us>.
>I immediately rule out the interpretation in which  `<#pat> denotes China, 
>`contact:mailbox` denotes geographical inclusion, and 
><mailto:phayes@ihmc.us> denotes France.
>To take an arbitrary example.).
>>So, picking up your line of consistency and experimentation, if an 
>>"identity" is derived from (is the set of denotations according to) a set 
>>of interpretations that are consistent to some level of observation, we 
>>always have the possibility that additional observations will detect 
>>inconsistencies, hence fragment the identity into several distinct 
>>"sub-identities", each derived from a subset of the interpretations of 
>>the original.  In this sense an "ideal" identity (e.g. in the sense 
>>intuitively/informally used for URIs) might be derived from the limit of 
>>some set of consistent interpretations as the number of observations 
>>considered tends to an infinitude of all possible observations.  That is, 
>>we can never know the identity completely, but may know it well enough 
>>for any given purpose.
>(I am reminded of a playground argument, "How do I know you don't see red 
>as what I see as blue.  You would call it blue, because everything I see 
>as blue you would say was blue when in fact it would be red." While that 
>which is "really" denoted can never be itself measured, it doesn't make 
>any difference)
>>(In saying this, I'm trying to paraphrase in non-mathematical terms the 
>>way that definitions of limits and continuity are used in differential 
>>(Reviewing what I wrote here, it seems that a corollary is that any 
>>identity corresponds to (or may in general correspond to) an infinite 
>>number of possible denotations.  I think that underscores the point about 
>>not assuming a single interpretation.)
>For me what underscores the need for being aware of possible differences 
>in denotations is the actual possibility that new information may turn up 
>distinguishing two things.
>However the danger of being too aware off it is that we spend too much 
>time worrying about it, like the kids worrying about what people really see.
>Another danger is that we loose the *intent* that URIs should be used to 
>represent globally unique things.  For example, if this talk of multiple 
>interpretation allows sloppiness in modeling for example peoples' home 
>pages, people's mailboxes, and people themselves in the knowledge 
>representation, then automated inference is doomed.

Graham Klyne
PGP: 0FAA 69FF C083 000B A2E9  A131 01B9 1C7A DBCA CB5E
Received on Tuesday, 22 July 2003 10:34:53 UTC

This archive was generated by hypermail 2.4.0 : Friday, 17 January 2020 22:56:00 UTC