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Re: How will the semantic web emerge

From: Frank Manola <fmanola@acm.org>
Date: Tue, 20 Dec 2005 17:14:52 -0500
Message-ID: <43A8825C.6030900@acm.org>
To: Henry Story <henry.story@bblfish.net>
CC: Joshua Allen <joshuaa@microsoft.com>, semantic-web@w3.org

I don't think this is necessarily the use of rdf:type that the OO vs. 
duck type distinction is really about.  If all you mean to do by 
identifying something as being of a given type is to indicate that it is 
a member of a set of things having a common characteristic associated 
with the set (and this certainly is the semantics of rdf:type), 
"thiefness" in this case, that by itself doesn't stress the alternatives 
too much.  But are you also going to describe :p as being blue by saying

   :p rdf:type x:blueThing.

as being 6 feet tall by saying

   :p rdf:type x:sixFeetTallThing.

and so on?  Most of the time, people are bundling a whole lot more into 
the notion of "type" than simple set-inclusion semantics, and that's 
where the problems often arise.  For example, most people would use

   :p ex:color "blue";

(or some datatyped variant) in the first example instead of using 
rdf:type, and what they have in mind when they make that distinction is 
often very significant.

At the same time, a slightly different interpretation of the example 
does get into the OO vs. duck type distinction.  Suppose the two 
statements in question are

   :p rdf:type x:thief.

and the other is

   :p rdf:type y:honest.

(because two people are making the statements, they each use their own 
type systems, x and y).  Now the issue isn't about which authority to 
trust, it's about what type system to use, and I needn't use either one, 
or I could use both.  After all, the same person might be a thief 
according to one person's type system (say, that used by the music 
industry) and honest according to another's (say, that used by the 
American Civil Liberties Union) without contradiction;  and all the 
other data about that person might be exactly the same.

--Frank

Henry Story wrote:
> Oh, you are worried about typing because it may lead you to have to  
> make decisions about which authority to trust. That is a problem of  
> database consistency not of typing. If two people say something  
> different about someone, such as
> 
> :p rdf:type x:thief.
> 
> and another says
> 
> :p rdf:type x:honest.
> 
> You will need to decide what you should add to your database. And  there 
> will always be many ways you can render your database  consistent. You 
> can either reject one or the other proposals, or  reject the proposal 
> that a man cannot be both honest and a thief.
> 
Received on Tuesday, 20 December 2005 22:13:51 GMT

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