W3C home > Mailing lists > Public > uri@w3.org > April 2003

resources, stuffs and individuation

From: pat hayes <phayes@ai.uwf.edu>
Date: Mon, 21 Apr 2003 16:43:52 -0500
Message-Id: <p05111b07bac9fe001b47@[]>
To: uri@w3c.org

Greetings.  After sending my recent message asking y'all to clarify 
the terminology of 'resource' and what is meant by 'having identity', 
I have read more of your archived discussions.  I now see that my 
previous message is capable of being misunderstood, so am writing 
this to help clarify my intended meaning.

I was using the words "identity" and "thing" in their senses as 
commonly used in philosophical logic and linguistic analysis.

First, by "identity" I mean that property of something which 
individuates it from all other entities; the property of being 
identical to itself, to the entity in question.  This is the sense 
used throughout mathematics and formal linguistic analysis and most 
technical philosophy, as well as modern ontology design, eg as in the 
term "identity criteria" used by Guarino and Welty. In particular, I 
did not mean it in a sense in which "having an identity" means 
"having been identified", ie in a sense in which to have an identity 
is to be referred to explicitly, or to have a means by which the 
entity in question can be located or singled out from other things. 
Thus, for example, each of the sodium atoms in my body has an 
identity - it is identical to itself - in the first sense, even 
though none of them has an identity in the second sense, since we 
have no agreed-on scheme for referring to individual atoms (and there 
are too many of them to keep track of, in any case).

Since I am fairly sure that many readers will understand the phrase 
"having an identity" in the same sense I have been reading it, I 
repeat my request that if you intend it to be read in some other way, 
to please clarify this other sense by expanding on the definition, 
perhaps with some supporting text.

Second, I do not take the word "thing" (as in "something" ) to refer 
merely to objects, but rather to any entity whatever that can be 
referred to by a noun phrase in English (at least). This includes 
'stuffs' (copper, igneous rock) (cf. the thread at 
http://lists.w3.org/Archives/Public/uri/2002Sep/0019.html ) as well 
as entities like categories of evanescent and dynamic phenomena 
(cirrus cloud formations; forked lightning), the phenomena themselves 
(the lightning stroke that hit the tree in my back yard last year) 
and abstractions (the complex plane; the notion of motherhood, the 
quality of mercy), and so on; anything at all that can be mentioned 
and be related to something else.  So to be "something" does not 
connote any kind of exclusion of what might be called non-object 
entities, or a restriction of the universe of discourse so as to 
exclude continua or continuous entities such as regions of some phase 
space.  In fact, the "somethings" one is obliged to consider go 
beyond English noun phrases. Often, the practical requirements of 
ontological reasoning require one to invent entire categories of 
entities which do not have any natural English translation, such as 
the 4-dimensional spatiotemporal envelope of an event (forming a kind 
of causal bounding box for fault analysis) and also to make finer 
distinctions than English does (eg CYC has about a dozen distinct 
senses of "cover".)

All of these things "have an identity" in the above sense, although 
of course the identity criteria differ between categories; for 
example, copper and igneous rock differ in their density and 
conductivity, for example, which are properties of stuffs.

(I don't mean to give the impression that there are no problems about 
'having an identity'. There are examples, widely discussed, of 
entities whose identity criteria are hard to pin down precisely, eg 
the Australian outback has no very clear spatial boundaries. But (a) 
there are many options for handling such things in practice, ranging 
from treating them as predicates to thinking of assertions about them 
as hidden quantifications, and (b) these difficulties often cut 
across other categorical distinctions, eg there are "outback" 
examples for events, stuffs, properties and times as well as for 
spatial regions.)


If I may briefly urge one or two substantive point here, rather than 
merely ask for clarification.

First, I would suggest that the best road for the WG to take on 
issues like these would be to be as agnostic as you feel you possibly 
can be about the exact nature of 'resources'. Your own email archive 
clearly indicates, if the point needed making, that the range of 
entities which someone might want to refer to by a URI reference is 
likely to outstrip the imagination of any of us. Already, from 
current work on mapping existing ontologies for use on Web, we know 
that we need to allow entities such as categories of wine, 
time-intervals, locations, leap seconds, real numbers, surface 
terrain textures, artistic styles and movements, and so on, as things 
that can be one way or another 'indicated' by a URI reference; not to 
mention such metaphysical exotica as eventualities (entities which 
represent the truth of a proposition in a spatiotemporal or other 
context), situations (contexts defined by a certain set of pieces of 
information) and continuants (3-d entities with changing properties 
and dynamic identity criteria). To emphasize, I am not making any of 
this up: all of these, and many others, have arisen in actual 
ontological practice.  Any attempt to legislate the ontological 
boundaries of all uses of URI references seems likely to create a 
problem somewhere; and I would suggest that unless you feel that 
there is an urgent need to impose some kind of limitation, that you 
take particular efforts to avoid using language which could be 
understood as imposing any such restriction.

Second, it is important for almost all reasoning engines that the 
general picture, of how URIrefs relate to whatever it is that they 
refer to, should also allow for the existence of similar things which 
are not referred to. That is, please do not say anything which 
restricts the universe of discourse to include only those things that 
have a URI or URI reference assigned to them (in whatever sense of 
'assigned' is appropriate.)  The reason for this request is that such 
a restriction effectively makes it impossible to use quantifier 
reasoning - that is, all kinds of formalized reasoning invented since 
about 1880, including most reasoning software - over the set of 
resources, so defined. The alternative logics that would be required 
(those with a "substitution interpretation" of the quantifiers) have 
been fully analysed and are known to be inadequate. This would be a 
crippling decision.

( I have the impression - ignore this, and please forgive me, if this 
impression is mistaken - that some members of the WG feel that this 
is a local problem with RDF (the 'blank node' issue) and therefore 
not of central importance, perhaps a matter private to RDF. Such an 
impression is however quite mistaken: it is central to an entire 
range of applications, and is not just a local RDF 'problem'. Since 
my voice may be tainted with an association with RDF, I urge you to 
seek other opinions.  )

Thanks again for your attention.

Pat Hayes

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Received on Monday, 21 April 2003 17:43:57 UTC

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