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Re: The meaning of "representation"

From: Xiaoshu Wang <wangxiao@musc.edu>
Date: Tue, 04 Dec 2007 22:43:24 +0000
Message-ID: <4755D80C.7070304@musc.edu>
To: noah_mendelsohn@us.ibm.com
CC: Chimezie Ogbuji <chimezie@gmail.com>, Mikael Nilsson <mikael@nilsson.name>, Tim Berners-Lee <timbl@w3.org>, www-tag@w3.org

noah_mendelsohn@us.ibm.com wrote:
> Xiaoshu Wang writes:
>> I am not sure if I have misunderstand. Do you want to say that 
>> "information *is* bit-stream"?
> Long ago Dan Connolly proposed what I think is often a pretty good rule of 
> thumb for contributions to this list[1]: "If a thread goes back and forth 
> three times without anybody suggesting textual changes to the document, 
> something's wrong."  I like that guideline, and I think we should take it 
> as advice to wrap up at least this little bit of the discussion, perhaps 
> without agreement if necessary. 
> Still, you've asked a direct question, so I think that deserves at least a 
> try at a direct answer:  No, I don't think I'd say that the "information 
> is the bit stream".  The way I understand Shannon, we can start by 
> imagining, as an example, a fixed set of messages I might wish to convey 
> to you:
> 1. The light is red.
> 2. The light is yellow.
> 3. The light is green.
> 4. The light is off.
> We know in advance that these are the possible messages.  If I, using some 
> code or other, manage to tell you that, for example, the light is green, 
> then we can say I have conveyed to you that information.  Now, as someone 
> who is interested in semantics you might say "which light?  what do you 
> mean by green?  Were you trying to distinguish regular green from dark 
> green, or did you mean any shade of green is OK?"Both Shannon and I, for 
> purposes of this exchange are saying: "Frequently the messages have 
> meaning; that is they refer to or are correlated according to some system 
> with certain physical or conceptual entities. These semantic aspects of 
> communication are irrelevant to the engineering problem."  They're not 
> irrelevant to the semantic web, but I think they are not essential to the 
> fundamental notion of information, is in "information resource". 
> All that's required here is that you and agree that they are four choices, 
> which we agree to label with the sentences above.  Now, we may have taken 
> the trouble to agree on very exact semantics for, say, the color green, so 
> you'll know exactly what frequency my light color will be.  Other 
> communities may be much more informal about it.  The Web allows both, 
> though I don't doubt that the semantic Web will allow much more precise 
> reasoning to be done when people define their RDF properties have 
> carefully defined and communicated semantics, rather than loosely or 
> informally defined ones. 
> Getting back to your question, I don't think the bits are information. One 
> encoding for the above information is as 2 bits per message, 00 = the 
> light is red, and so on.  Shannon points out that this is an optimal 
> encoding bandwith-wise only if the 4 choices are equally likely, but we 
> don't care about that.  You and I could instead agree on a more verbose 
> encoding, such as the UTF for the characters RED = The light is red, GREEN 
> = The light is green, and so on.  I would say that the bits for this 
> coding are very different (UTF 8 vs little 2 bit sequences) but the 
> information conveyed is the same.
> Going a bit further, I can pretty well signal my views on information 
> resources using this example:  Let's I as the owner of 
> http://example.com/lightStatus decide that I want to assign that URI to a 
> URI which has as its state the 4 way choice above.  It knows that a light 
> is either red, green, yellow or off.  I believe that I can fully convey 
> the essence of that resource in a message (I've just shown at least two 
> ways), so it's an information resource.  It doesn't matter whether I had 
> in mind some particular real world traffic light, some rigorous definition 
> of the color green, etc.  It's a resource that can answer a question one 
> of 4 ways, and it's an information resource.  I might instead be thinking 
> of a real actual traffic light, the kind that will actually bend your car 
> if you run into it.  That's not an information resource, because I can't 
> use messages to bend your car as it runs into the light.  The thing has 
> mass and is screwed down to the street.  If I want to put up on the Web a 
> resource that tells you whether that light is red, yellow, green or off, I 
> should use a 303 redirect from the URI of the big heavy light itself.
Noah, I am lost.  I don't think we disagree anything there.  But I am 
not sure what is your point.  If I have a URI say,
http://example.com/trafficelight to denote the traffic light in front of 
my office.  You said that you want me to 303 to your 
http://example.com/lightStatus, how? You need four URI for that.  
Second, what if I want to describe the hight, or material, or other 
information of that traffic light.  What am I going to do?  How do I 
know what a user want?

Received on Tuesday, 4 December 2007 22:44:06 UTC

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