W3C home > Mailing lists > Public > xml-uri@w3.org > May 2000

Re: Syntax and semantics

From: Tim Berners-Lee <timbl@w3.org>
Date: Wed, 17 May 2000 18:03:27 -0400
Message-ID: <00db01bfc093$436521d0$b0ec5c8b@ridge.w3.org>
To: "W. E. Perry" <wperry@fiduciary.com>, "Paul Prescod" <paul@prescod.net>, <xml-uri@w3.org>
Thank you, Walter Perry, for defining semantics and distinguishing it from
syntax.   I am happy with those definitions.

I continue to agree with your message up to a point, where my model for
communication
and yours are I think basically the same but applied differently to this
question.

I believe that an XML document has semantics. It has meaning. (in
general!...)


>>  * if semantics are entirely local, then does Microsoft have the right
>> to interpret the "a" element type in xhtml as meaning "archive" and the
>> "b" as meaning "Beethoven"?
>
>Absolutely, if they can implement desirable behavior from a process by so
assuming.

I would disagree. I would say that there are a set of understandings which
are
broken when that happens. Also, the system has broken here. The author of a
document uses <b>poison</b> for emphasis and the browser puts up a picture
of Beethoven. The reader of
the document does not notice the phrase and drinks the poison. Whether you
regard that as
desirable or not, it was not the semantics of the message. It was not "that
signified".

That is not the way the Web is designed IMHO.  The Internet is designed on
the
assumption that using common languages such as English we come to define
protocol
specifications which are generally considered to be well defined. This
specifications
define new languages (such as xml namespaces) where a syntactically valid
sentence has a
semantics which is then indirectly defined though the language spec.  You
find the semantics by applying the
definitions from the specification to the particular combination of terms
chosen by the document
author.  The semantics is a form of product of the syntax of the document
and the semantics of
the specification of the namespace used.


In that model the specs are all grounded in English which is assumed a
common language. English itself
is defined in a complex self-referential way with few actual connections to
anything physical.
The web might slowly work its way in that direction as more an more semantic
links between
languages are created but let's not get into that now.

But the identity of the namespace is obviously key.  So is the concept of
"grounded documents"
where a grounded document is one in some chosen base set or another document
defined in
terms of grounded documents.  For example, a good web site's web pages are
grounded in
W3C Recommendations.


>> If they write a web browser that archives
>> any link you click on and play's music for bold, will you defend them on
>> the basis that semantics are local?
>
>No. If I want that behavior I will buy their software or use their process
(or to use Tim
>Bray's terminology, dispatch to it from my local node).


I prefer to talk about what things mean without discussing behavior. I agree
with you
that you can read a book, understand well what the writer meant, but behave
in a great
variety of ways as a result.

>> I think that behavior is local, but
>> semantics absolutely must be shared.
>
>Not shared a priori. That is the single great lesson to be drawn from the
Internet topology
>of autonomous, largely anonymous nodes which, when they act must treat one
another as peers
>because they do not know enough about each other to infer any other
relationship. Semantics
>are effectively negotiated in the instance, and the ability of two nodes to
negotiate a
>successful transaction, understanding, or other disposition of given
content on one occasion
>implies NOTHING about their likelihood of reaching a similar conclusion, or
any conclusion at
>all, with analogous content on a subsequent occasion (this really is a
Heraclitan cosmos).

You rule out the ability to make a promise. But you talk about negotiation.
Negotiation normally implies a conversation with a shared state.
I don't understand your model of how this works.  (In fact there are lots of
protocols make promises.  When you associate a uuid: with a document
you promise never to reuse it. When you order something you promise to
pay...)


>The vertical industry data vocabularies (FpML, ESteel, etc., etc.) which
have been the
>shining demonstration of XML's acceptance in the past year are predicated
on a closed-world
>view which is anathema to the real potential of XML as syntax. All of these
vocabularies are
>designed to convey intent, with the expectation that intent will be
correctly interpreted and
>result in the execution of a desired process.

I would say that the expectation is often that they are not misinterpreted.
Often a document is sent without the knowledge that it will be understood.
As you say, to be assured in advance requires a promise.
But when you send me a message grounded in documents I am
aware of I can infer from it an equivalent message I can understand.

> It is only in a closed world
(a cartel, to put
>it bluntly) that those expected processes could be assumed to be generally
known and
>generally considered desirable activities. In the Internet topology we
simply do not have
>enough knowledge of our fellow nodes to make such assumptions, but we may
well have the
>desire to do business with or otherwise communicate with them.

This is surely a statement about social groups not about the Net.
There are many groups which share languages apart from cartels.
Everyone using a certain proprietary word processor forms such a group.

> In order to
do so, we could
>first attempt to indoctrinate them in the shared assumptions and accepted
premises of our own
>milieu, but that might not work:  they may prove recalcitrant; it may turn
out they are more
>influential than we within the larger Internet universe; or they may simply
not give us their
>attention, or understand what we are trying to communicate. That is where
the value of the
>Semantic Web becomes apparent. One pair at a time, autonomous nodes can
build the semantic
>context within which they come to understand one another. I will not
elaborate on this
>process now; I have done it at plenty length elsewhere.

huri me an uri?

>The only point to make now is that
>the negotiation must be based on each node handed the other semantically
neutral content.

I don't know what "semantically neutral content" is.  Messages which do not
mean anything?
That doesn't help me make sense of your position.
[...]


Tim BL

(apologies for the varying time delays - I am on and offline at Amsterdam)
Received on Thursday, 18 May 2000 02:33:38 UTC

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