Re: what RDF is not (was ...)

From: Sandro Hawke <>
Subject: Re: what RDF is not (was ...) 
Date: Wed, 02 Jan 2002 15:36:22 -0500

> >Peter F. Patel-Schneider:
> > > Sandro Hawke:
> > > RDF is a language for transmitting pieces of collaborative databases.
> > > It started as a way to categorize web pages, but since the subject
> > > matter of the web is arbitrary, RDF ended up as a way to express
> > > arbitrary information, just like one might store in a relational DBMS.
> > > The pieces of RDF are pieces of a web-wide database of information,
> > > not just about web pages but about anything.
> > 
> > Well sort of.  RDF cannot express arbitrary information, of course, and
> > neither can a DBMS.    You indicate that this is the case below,
> > contradicting your statements in this paragraph.
> It's so hard to write for a general audience and a technical one at
> the same time.  Still...  I didn't say RDF could say anything about
> anything, just that RDF could say something about anything.  Do you
> disagree even with that?  

My reading of ``RDF ended up as a way to express arbitrary information'' is
that if I take any information then RDF can express it.  As far as RDF being
able to ``say something about anything'', I'm deeply pessimistic about even
this ability.  In particular, how can RDF say something a particular
arbitrary real number?  There just aren't enough URIs to provide names for
them all.

> In any case, I meant that sentence to be
> more evocative than technical; when I'm being pedantic, I'm not
> exactly sure how bits ever say anything.  How about:
> "The pieces of RDF are pieces of a web-wide database of information,
> no longer just about web pages, but containing whatever information
> people want to share in a database format."
> (still not pedantically correct, of course.)

Yes, this is closer to something that I might say about RDF.n

> > [You may be thinking that information is different from knowledge.  If so,
> > I would like to hear how you make the distinction.]
> > 
> > > While SQL is a database manipulation and query language, RDF is just a
> > > data format, equivalent to the tables that result from a SQL query or
> > > to an on-disk database file format.  (RDF still needs a SQL-equivalent
> > > language.)  RDF's database model is different from SQL's in being
> > > "webized" to support distributed collaboration: tables/columns and
> > > datatypes are named in a global namespace (URIs) so they can be
> > > automatically linked.
> > > 
> > > There is a temptation to think a mass of RDF fragments can store all
> > > of human knowledge.  The truth is that RDF is only marginally better
> > > than a typical SQL database for storing "knowledge".  It works well
> > > for a catalog of the CDs you own, or the products you sell, or the
> > > configurations of software installed on your computers, but the only
> > > thing it does for "knowledge representation" and "machine reasoning"
> > > is provide a standard underlying format.
> > 
> > I would like to know how RDF can provide a ``standard underlying format''
> > for knowledge representation, in a way that is different from the way that
> > sequences of bits can.
> It's got lots self-description, which seems to be helpful sometimes.
> (as mentioned in the next paragraph....)

Sure self-description can, sometimes, provide benefits, but does it really
go any way to providing a ``standard underlying format'', particularly as
RDF is so weak.


>     -- sandro


Received on Thursday, 3 January 2002 19:57:01 UTC