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Re: How does RDF/OWL formalism relate to meanings?

From: Dan Connolly <connolly@w3.org>
Date: Thu, 08 Apr 2004 16:42:03 -0500
To: Pat Hayes <phayes@ihmc.us>
Cc: John Black <JohnBlack@deltek.com>, public-sw-meaning@w3c.org
Message-Id: <1081460522.16761.11584.camel@dirk>

On Thu, 2004-04-08 at 15:23, Pat Hayes wrote:
> >On Tue, 2004-04-06 at 20:53, Pat Hayes wrote:
> >[...]
> >>  But the direct answer to your question is that we don't really have a
> >>  way to do that, actually, yet. Not a fixed, standard way. And IMO,
> >>  until the TAG group gets its communal head out of the sand, or
> >>  whereever it has it located,  we never will, because the TAG group
> >>  thinks that URIs are already anchored to "resources" which they
> >>  uniquely "identify",
> >
> >I don't understand why you find this notion novel, let alone
> >disagreeable.
> 
> I don't. Its called naming, or identification. its a very useful and 
> powerful idea. The problem is that the TAG group seems to think that 
> it just kind of happens, or maybe is just kind of true, so doesn't 
> need to happen, or something.

Ah... so perhaps I parsed the head-in-the-sand comment as
attached to the wrong bit... ok...

>  Take the architecture doc draft: it 
> just ASSUMES that it is meaningful to talk about the resource 
> identified (named) by a URI, that URIs and resources have owners, and 
> so on, all without explanation or even introduction.

Well, we introduced URIs in a way that we thought was fairly typical
of the way most people are introduced to them:

[[
While planning a trip to Mexico, Nadia reads "Oaxaca weather
information: 'http://weather.example.com/oaxaca'" in a glossy travel
magazine.
]] -- http://www.w3.org/TR/webarch/#intro

>  But nobody says 
> anything about how all this structure of naming and ownership is 
> actually handled: there are no protocols for naming things or for 
> claiming ownership of URIs.

The typical protocol is: you register a domain name and
set up a web server and then announce it thru existing
communications channels.

We discuss that very briefly:

[[
The requirement for URIs to be unambiguous demands that different agents
do not assign the same URI to different resources. URI scheme
specifications assure this using a variety of techniques, including:

Hierarchical delegation of authority. This approach, exemplified by the
"http" and "mailto" schemes, allows the assignment of a part of URI
space to one party, reassignment of a piece of that space to another,
and so forth."
]]
 -- http://www.w3.org/TR/webarch/#uri-ownership

Do you think it would help to elaborate on how the weather service
registers its domain and such?



> In fact, naming is complicated, and in broader human society is 
> surrounded by legally defined protocols and rituals and prohibitions. 
> Like I said at the Boston plenary, there is no notion of baptism on 
> the Web; and until we get one, there really aren't any names on the 
> Web.

Doesn't the section on uri ownership cover this, if somewhat
briefly?

Are you using 'baptism' in some technical sense? or just the
conventional sense of "A ceremony, trial, or experience by which one is
initiated, purified, or given a name."

http://dictionary.reference.com/search?q=baptism&r=67

>  (Arguably, the connection between an http: URL and the thing you 
> GET when you use it with the right protocols could be said to be a 
> naming, and the Web itself is the baptising "authority".

That appeals to me. In fact, does it really need saying at all?
Isn't it obvious?

>  That makes 
> sense for http: URLs, but isn't much help for RDF or OWL.)

OK, now you've lost me. What difference does it make to RDF
or OWL whether the names start with http: or ftp: or mailto:?
If it works for http: URIs, why not the rest of them?
Why not in RDF/OWL?

> >Names denote things.
> 
> Yes, but they don't JUST denote things. They denote things rigidly, 
> in special ways. They NAME them, in the actual world, not just 
> relative to an interpretation.  To claim that my name is "Bill 
> Murray" is just plain flat wrong, even if you are willing to think 
> about an interpretation in which "Bill Murray" denotes me.

"just plain flat wrong"... now that's a new one.

I'm familiar with the leves of truth discussed in
logical literature such as

  Three Levels of Truth
  http://www.earlham.edu/~peters/courses/logsys/3levels.htm

but I'm not familiar with that one.

The only way I know to relate claims like saying your
name is "Bill Murray" to ... er... actual reality
is with economics and utilitarian measures. i.e.
you haven't agreed to answer to the name "Bill Murray"
so if I want to get your attention, calling out "hey Bill Murray!"
is not likely to help me much. And if the police want
to catch a criminal called "Bill Murray" they'll be
wasting their time if the go to your house, and so on.


>  Names 
> play a special role in communication.  And in any case its not at all 
> clear that what the TAG means by 'identify' really is denotation.

No, it's not all that clear how it relates to Tarski and such.
I hope we'll figure that out in the coming months/years.
But I think the document isn't totally useless in its
present state.

> >It's a recurring pattern
> >in languages. For example, in SCL:
> >
> >
> >A nonempty set UI called the universe;
> >A mapping intI from VO to UI;
> >
> >-- http://www.ihmc.us/users/phayes/SCL_current_2004_rf.html
> >
> 
> Nothing there about naming.  SCL hasn't got any names in it (except 
> maybe things like datatype URIs, arguably.)

This use of 'name' is new to me. I had previously considered
names to be just a kind of term, i.e. a syntactic device.

For example, you/we wrote:

"for example, this semantics assumes that names denote things in a set
IR called the 'universe'"
  -- http://www.w3.org/TR/rdf-mt/

But now you're saying, pretty emphatically, that there's some other
notion of naming that you think webarch should discuss, yes?

> >The webarch document is written in much less formal terms,
> >but it's the same idea.
> 
> No, its NOT. Its a different idea. Names refer, but all reference 
> isn't done with names.
> 
> >The webarch document suggests
> >an idealization where there's just one interpretation,
> >but that's just an idealization.
> 
> That is not an idealization for GET applied to URLs.  There is a 
> genuine notion of identification, and for URLs indeed it is an 
> architectural requirement that URLs really do identify in this sense: 
> its vital that the identification be unique in that case. URLs really 
> are like Web names, but only for Web resources.

'Web resource' is the universe of discourse, no? Ah... perhaps
you mean resources that are on the Web in the sense of...

[[
Note: The Web Architecture does not require a formal definition of the
commonly used phrase "on the Web." Informally, a resource is "on the
Web" when it has a URI and an agent can use the URI to retrieve a
representation of it using network protocols (given appropriate access
privileges, network connectivity, etc.). See the related TAG issue
httpRange-14.
]]
 -- http://www.w3.org/TR/2003/WD-webarch-20031209/#dereference-uri

I think TimBL, the leading proponent of making that distinction
in the webarch document, prefers the term 'Information resource'.

You seem to be arguing in the same direction. But I'm not sure
I see an argument clearly enough to convince other TAG members.


>  The TAG seems to be 
> talking about that notion (or a Webbish version of it) most of the 
> time, which is fine; but that's one idea, and reference is a 
> different idea. The TAG seems to be confused about this distinction.

Well, undecided, at least.

> >If you like, look
> >at a webarch:resource as a mapping from an SCL
> >interpretation I to an element of U[I].
> 
> Well, I tried that, but then 95% of what the architecture document 
> says doesn't make any sense. For a start, if the entire architecture 
> document is supposed to be relative to an interpretation, how does 
> anything ever use the internet to communicate? You can't send an 
> interpretation over the web.

no, only representations.

> BTW, if this is right, then there *really* are no names on the Web, 
> since even http: URLs aren't names if they denote only w.r.t an 
> interpretation.

I'm not sure how best to view it. Web architecture works
best if they really are rigid, but it degrades fairly gracefully
if, on rare occasion, a few of them are not.

> >Or look
> >at each protocol message as carrying its own interpretation
> >or something. It doesn't matter that much. The webarch
> >document doesn't constrain things that formally; it
> >uses more utilitarian/economic descriptions such as...
> >
> >
> >"a resource should be assigned a URI if a third party might reasonably
> >want to link to it, make or refute assertions about it, retrieve or
> >cache a representation of it, include all or part of it by reference
> >into another representation, annotate it, or perform other operations on
> >it".
> >  -- http://www.w3.org/TR/webarch/
> 
> That's NOT a more utilitarian way of talking about Tarski: it is 
> something else altogether. It uses the words "assigned to" for 
> example which has no meaning in a Tarskian semantics. (It also talks 
> about linking and retrieving and performing operations on resources, 
> which opens a whole other can of worms.)
> 
> This is exactly the point where John's question has some force: HOW 
> does one assign a resource to a URI?

Use the resource in communication protocols.

>   What do you DO to get the 
> assignment done?

Most typically: register a domain name and set up a web server.

>  If you are inside a single interpretation, this 
> makes no sense: the interpretation has already assigned a denotation 
> to the URI. If you aren't inside a particular interpretation then 
> presumably this would be done, classically, by restricting the set of 
> interpretations by making suitable assertions, right? But how can you 
> attach a unique referent to a name by making assertions (in OWL, 
> say)? All you can do it to relate URI referents to other URI 
> referents. You have to have some referring names to get the process 
> started.
> 
> Analogy.
> OWL and its MT lets you draw maps. You can get the shapes right that 
> way. What you can't do just by drawing maps is set up the coordinate 
> system that a map uses to anchor itself to a position on the actual 
> planet, the latitude and longitude.  That requires some conventions, 
> some agreements about where exactly the origin is and how long a 
> degree is and which way is north.  We don't have these conventions 
> yet for reference on the Web. (Well, maybe URNs provide some, but 
> they don't seem to get used very much.)
> 
> >  >  and so refuses to think about the fact that they
> >>  aren't, and what to do about it.
> >
> >Oh bull-pucky. There are megabytes of evidence to the
> >contrary. The TAG thinks about it a lot,
> 
> I havnt seen anything in any of the TAG archives that addresses the 
> issue John was referring to, which is how to assign a name to a thing 
> (not a resource, a THING.  Like a person or a company or a star.)  (I 
> havnt read them ALL, however, I admit)

[Again: 'resource' is the universe of discourse, so I'm not sure
how to take "not a resource, a THING". Presuming you mean
"not an information resource" or some such...]

I think we're agreed that, in general, one assign names to things via
communication protocols.

But beyond that, lots of people disagree...

One position on httpRange-14 is
that to assign a URI to a person, you refer to that person
using an expression in some language like RDF or OWL...

  <foaf:Person rdf:ID="DanC"> ... </foaf:Person>

and you use that RDF document as the representation of some
information resource, say http://www.w3.org/People/Connolly/home-smart .
Then the expression http://www.w3.org/People/Connolly/home-smart#DanC
is an expression for "whatever DanC means in representations
of http://www.w3.org/People/Connolly/home-smart".

But another position on that issue is that, for example,
http://www.markbaker.ca/ is a name for Mark Baker because
it's his URI and he says so.


> But If Im wrong Id be delighted to be told where to look.

The discussion history of this issue is long:

"Discussion history
        1 Jul 2002, 15 Jul 2002, 22 Jul 2002, 29 Jul 2002, 16 Sep 2002,
        24 Sep 2002, 6 Jan 2003, 27 Jan 2003, 6 Feb 2003, 23 Jun 2003,
        22 Jul 2003, 28 Jul 2003"
http://www.w3.org/2001/tag/issues.html#httpRange-14

I remember a particularly intense discussion in Irvine, but I can't
find a record of it. The record from Vancouver is pretty good...
http://www.w3.org/2002/09/24-tag-summary#httpRange-14

Ah... there's the Irvine record
 http://www.w3.org/2003/02/06-tag-summary
in particular, section
 3.2 URIs, Resources, Identification (httpRange-14)
 

>  (And in 
> that case I reckon that the architecture document ought to say 
> something about this, BTW.)
> 
> >and TAG
> >members have thought about it and written about it
> >for at least 10 years, and I'm not aware of any
> >indication that it will stop.
> 
> All I keep hearing is that URIs 'identify' resources. Nobody EVER, 
> EVER says what in hell's name a "resource" is supposed to be (why 
> can't the TAG speak English like the rest of the planet?

Perhaps because it's a 9-headed beast, not a single person?

>  I know YOU 
> have an answer, Dan, but your answer makes the architecture document 
> incoherent) or what exactly they mean by "identify". As far as I can 
> tell, what Roy means by "representation" in the REST model is 
> something completely different to what everyone in KR or linguistics 
> means. Which would be fine, if we could get the distinctions clear: 
> but we don't have it clear, and the TAG group just uses the word 
> without ever clarifying what sense of it they are using, and often 
> with no apparent awareness that there are multiple meanings that need 
> to be distinguished.

We're very, very painfully aware. I don't think actual blows
have been exchanged, but very close to it. The issue was
"postponed" for a while because we were unable to discuss
it civilly.


> I have made several carefully worded requests for definitions or even 
> just for clarification. So far the best response I've gotten is from 
> Tim, who tells me that this is an "issue" that the TAG decided to 
> postpone. Speaking clearly and saying what you mean is an "issue" ?? 

Absolutely.

> Using words carefully and explaining what you mean by them in order 
> to communicate properly is not an "issue": it's English composition 
> 101.

Haven't you been working in groups long enough to appreciate
how difficult it can be to achive consensus on something like
this?

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
see you at the WWW2004 in NY 17-22 May?
Received on Thursday, 8 April 2004 17:41:31 GMT

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