Hi Pat --
You wrote....
At least four distinct logics for
context have been fully developed and at least two of them are now
deployed in industrial-scale working software systems.
Most interesting. Do you have references that describe what the deployed ones are doing industrially please?
Thanks! -- Adrian
Internet Business Logic
A Wiki and SOA Endpoint for Executable Open Vocabulary English
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Adrian Walker
Reengineering
On 1/2/08, Pat Hayes <phayes@xxxxxxx> wrote:
> > [DN] Would make an interesting ontolog session sometimes in 2008.
>> Maybe Peter can schedule a call.
>
>[ppy] Sure, I'd be most happy to. I'd need a more refined statement of
>WHAT (exactly) it is, that folks would like to discuss, and WHO are
>the people they would like to hear from (or hear discussing the issue
>at hand).
>
>Are we going for CL, CG, IKL and the relationship between symbols in
>the logical "universe of discourse" and individuals in the "real
>world"? Representing Context in general? How CL/IKL deals with
>context? ...
>
>I solicit input from those interested on:
>(a) A clear statement of the "topic",
FWIW, this is not a new topic. The general idea of the relevance of
context in language and KR and logic has been discussed now for
several decades, including at least one entire series of successful
interdisciplinary research meetings entirely devoted to it. At one of
the very first 'ontology summit' meetings (at Heidelburg in, if my
memory serves me right, 1997), a whole session was devoted to an
attempt to define and clarify the notion. At least four distinct
logics for context have been fully developed and at least two of them
are now deployed in industrial-scale working software systems. So we
are not, or at least SHOULD not be, working in an entirely new area
here.
Unless all the participants are at least marginally aware of all this
preceding effort and the general shape of the debates that have gone
on, we will only be repeating history.
FWIW, here is the definition of "context" that I put forward at
Heidelberg, and which seemed to meet with some general acceptance.
-------
Theories of meaning invariably focus their attention on some subset
of the many factors which can possibly influence the actual meaning
conveyed by a meaningful utterance or sentence or diagram, or any
symbolic structure or act. The other factors or aspects which may
influence meaning, but which are not explicitly examined by the
theory, are often referred to as "context". Thus, the term "context"
has no single meaning: it is used simply to refer to anything (or
sometimes everything) which can influence meaning but which is
outside the scope of the current theory. It is always defined
negatively.
-------
This means, in turn, that there is no such 'thing' as an objective
context, and so there is no general theory of contexts, or science of
contexts, which can be applied to all cases of "context". Indeed,
since, in the limit, it seems that almost anything can influence
meaning under some circumstances, it follows that anything at all can
be considered to be a context. One sees evidence for this conclusion
by examining the proceedings of any of the 'context workshops', and
checking carefully what each author means by the word "context". At
the second such workshop (held at MIT in 2003), every single
contributing author had a different notion, ranging in scope from a
single occurrence of a single word in a single sentence (as exhibited
in so-called 'priming' experiments) to an entire social/cultural
milieu, such as China in the 13th century.
Which, to get back to the topic, is why starting a discussion of
contexts with any attempt to "define the topic" is unlikely to
succeed, for the very good reason that there really is no such topic.
(And even if by some miracle it does, that success will only be
temporary, because you can guarantee that someone else out there will
disagree.)
BTW, partly as a reaction to this observation, the formalized
'context logics' developed by McCarthy, Guha (and John Sowa, though
he used a different terminology) are deliberately agnostic as to the
nature of "contexts", and adopt a theoretical stance along the lines
of: a context is whatever satisfies the axioms of my logic/theory of
contexts (analogous to a mathematical reply to a question such as
'what is a commutative algebra?'). However, the apparent
reasonableness of this 'mathematical' stance is somewhat undermined
by the fact that none of the extant such logics provide more than one
or two axioms or principles, and the very few that they have provided
have obvious, immediate counterexamples in cases that everyone agrees
should be possible to treat as contexts (such as a time-interval).
This situation has not changed in about a decade of intensive work on
these logics, which to my mind at least reduces the 'mathematical
theory' position to absurdity: apparently, there is no mathematical
theory of contexts. And calling a diverse collection of things by a
single name is not good science, nor good engineering, nor good
methodology. For example, a good deal of the work on "context logic"
has been a slow rediscovery of ideas that were already well known and
thoroughly investigated in temporal logic, but because it was seen as
being about "contexts" instead of mere time-intervals, the earlier
work (which in many cases was vastly superior, having been done by
some of the best philosophical logicians of the last century) was
ignored.
The more popular recent stance is that there are many kinds of
context, each with its own axioms and principles: time-intervals,
time-points, sets of beliefs, linguistic conventions, conversational
settings, etc.. Well, OK: but all of these (and others) already had
more or less mature fields investigating them, without using the
"context" word. So now the question arises, what value is gained by
using a single term to refer to them all? It suggests a commonality
which does not appear to be present. Time-intervals and states of
belief, in particular - the two most commonly suggested "kinds" of
context - seem to have almost nothing in common at all. If anyone can
suggest a single axiom which relates propositions or sentences to
contexts, and is true both when this means the proposition is true at
or in that time, and also when it means the proposition is entailed
by a set of beliefs, I would be delighted to be shown it. I have made
this challenge repeatedly to proponents of 'contexts' for many years,
and have yet to be given an answer.
Pat
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