RE: New Intro to RDF

Hi,

Thanks for this. I think it is particularly useful to distinguish RDF
from its XML serialization. 

I have a couple of comments, but I am not a regular contributor to this
list, so this is a personal view - please excuse me if I am out of
place.

Under the section "What is RDF" you say "RDF is nothing more than a
general method to decompose information into pieces". I think that this
cuts straight to the heart of two views of RDF.

On the one hand, RDF is commonly used and treated as a database of
information held in "triples". RDF has stimulated a lot of research into
databases built on triple stores, and for some applications these offer
significant advantages over conventional relational databases. I think
the research is very valid and interesting. I also think that this view
is the most likely to bring immediate benefits to a "Semantic Web". 

On the other hand, actually RDF IS more than this. It has a formal logic
which allows you to deduce, for example, that 

	<a foo b> implies <foo rdf:type rdf:Property>

This is pretty feeble on its own, but as you point out towards the end
of the article, RDFS introduces a wider vocabulary with a richer
semantics. The point is that the RDF semantics allow you to add extra
triples that were **not in the original data**. This is part of the
distinction between a database and an ontology, and I think this
distinction is worth some extra clarification. 



Secondly, I would like to make a comment about the use of URLs as unique
identifiers. This idea is central to RDF and is always included in a
discussion of its benefits, but this has been an area of some
controversy, and I think counter arguments deserve a mention. Some
counter arguments are

1. Names only have to be unique IN CONTEXT. For example, I can write a
program using variable x without any danger of interfering with your
program, also containing variable x. And in natural language, the phrase
"I am going to try to catch the plane" has a different meaning in the
context of an airport and the context of a woodwork shop, but there is
no difficulty in using the same word for two different things because
the meaning is clear from the context. 

2. Using URLS does not guarantee uniqueness. Many people may choose to
use the same URL to mean different things. 

3. By avoiding the problem of using the same word for different things,
you multiply the problem of using different words for the same thing,
and this problem is probably more difficult to resolve. 

4. Using URLs makes many people believe that the URL is an address of
some useful information, and this is not the case. They are just names.
The URLS can be completely fictitious. More dangerously, the content of
a URL can change over time. 

5. URLS make RDF difficult for humans to read and understand. The
problem is compounded by that fact that prefixes can be used in some
places but not in others. 

In other words, URLS are not a silver bullet, and I think the advantages
should not be overstated. 

Tim Glover




-----Original Message-----
From: semantic-web-request@w3.org [mailto:semantic-web-request@w3.org]
On Behalf Of Joshua Tauberer
Sent: 03 October 2005 23:22
To: 'SWIG'
Subject: New Intro to RDF


Hi,

As probably everyone on the list knows, there's a lot of negative 
opinions of RDF out there, and it seems like some of this stems from a 
confusion of RDF the XML format and RDF the general method for 
expressing knowledge.  But, I haven't come across a deep explanation of 
what RDF-the-method is that we can point people to so they know there's 
more to RDF than the serialization format.

I know such a document may very well exist, but I figured I would take a

stab at writing one myself.  (If it has no value for anyone else, at 
least I gained a deeper understand of RDF by writing it :-).  What I 
wrote is posted at:

http://taubz.for.net/code/semweb/whatisrdf/

The goal was to introduce RDF from the beginning, show why it's useful 
for modeling knowledge in a distributed way, and to give a basic 
presentation of RDFS and OWL.

It's long for an introduction as I tried to be as explicit as possible 
about what defines RDF (at least in my understanding of RDF).  A shorter

to-the-point version could be synthesized from this.

Comments welcome, especially if you think it was worth the time writing.
:)

-- 
- Joshua Tauberer

http://taubz.for.net

** Nothing Unreal Exists **

Received on Tuesday, 4 October 2005 10:02:48 UTC