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

>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?  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.)

> [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....)

> > (If RDF sounds a lot like XML, well, it is.  The difference is that an
> > XML database fragment is less self-describing than an RDF one.
> > Whether this difference is critical is a subject of debate.  Whether
> > either of them is better than a comma-separated-values file is also
> > subject to debate.  The basic question is whether self-description is
> > important.)

Personally, I'm not enamored of self-describing formats, prefering
self-identifying ones with external descriptions.  But I think I'm in
a small minority in the web community here, and it's probably not so
black & white as I make it sound.

    -- sandro

Received on Wednesday, 2 January 2002 15:39:16 UTC