W3C home > Mailing lists > Public > www-rdf-logic@w3.org > April 2001

RDF semantics: applications, formalism and education

From: Graham Klyne <GK@NineByNine.org>
Date: Tue, 03 Apr 2001 10:40:05 +0100
Message-Id: <5.0.2.1.2.20010403094420.00a65700@joy.songbird.com>
To: www-rdf-logic@w3.org
It is with great interest that I have followed the thread about the 
adequacy of RDF.  I think Peter F. Patel-Schneider captured a theme with 
these comments:

>1/ There are many places in the RDF and RDFS documents where vitally
>important statements about the semantics of RDF or RDFS are presented with
>no formal backup, and in a totally inadequate fashion.

[...]

>2/ The triple model does not provide sufficient representational power to
>transfer interesting semantic content.

While fully accepting both of these statements, I'd like to try and make a 
case for not giving up on RDF:


Regarding point (2):

I shall assume that by "interesting semantic content", a level of 
understanding about some domain of discourse adequate for the purposes of a 
range of reasoning activities is meant.  I guess this would be roughly what 
is required for software agents to negotiate autonomously and flexibly on 
behalf of their human "masters".

I think there is a range of applications for which the expressive power of 
basic RDF is adequate.  (e.g. RSS, calendaring, directory metadata, message 
metadata, web page metadata, etc., etc.)  I think these will typically be 
applications in which human participants are still directly involved.  For 
these applications, the expected value of using RDF is (a) to leverage 
common tools, and (b) to ease the movement of (RDF-coded) data between 
different applications, or to be able to combine data from multiple 
applications.  Prosaic stuff, but still valuable.

I also happen to think there are some simple rule-based systems (e.g. 
simple access control, directed searching, system component matching) that 
can be built using a kind of limited inference framework similar to that of 
RDF(S), which falls considerably short of FOL.

Where I think things get interesting is if we can use this dull old common 
metadata format as a foundation on which to build the more interesting 
semantic content and reasoning elements.  Because, if we can do this, the 
"semantically aware" components potentially have access to a wealth of raw 
data for their cogitations.

Then the question I ask is:  Is RDF adequate as a basis for building 
definitions of richer semantic capabilities?  (I don't ask if it's the best 
base to build from, or complete, just if it's an adequate 
foundation.  Someone reminded me recently that in the Internet standards 
area "the Best is the enemy of the Good".)  I think the answer to this 
question, from what the logicians among us have been saying, is "Yes".

I think there is value in the simplistic framework of RDG precisely because 
it is simple.  For an Internet standard I think it would be a mistake to 
build up the base RDF so that the simple functions are no longer 
simple.  Something I have learned is that Internet standards are often most 
successful when built in relatively small incremental stages.  I think 
that, roughly speaking, RDF is the right size of step and would resist 
trying to put full semantic expression (whatever that may be) into the RDF 
core.  The fact that we might build different semantic frameworks on that 
core is a real strength at this time.

I don't think this is anything not already said, but it seems to have been 
lost in the recent debate about the semantic adequacy of RDF.


Turning to point (1):

I think that, in some respects, the RDF specification is its own worst 
enemy, and that the lack of comprehensive formal underpinnings may be part 
of the reason.  As one who intends to be an active participant in the RDF 
review WG, I hope to do my part in rectifying this.  I believe other 
participants will do likewise.

But I think we have a significant job of education ahead of us:  (a) 
education of the specification writers in the subtleties of formal 
underpinnings (e.g. is it a "model"?  I know I have much to learn), and (b) 
education of the specification users;  this means being able to draft the 
specification in such a way that the expectations of system developers who 
don't have a background in formal systems are set appropriately.

I believe that truly outstanding experts in the field of logic and 
semantics are engaged here, and I truly hope that you will help us to get 
the formalities right this time, and to effectively communicate the 
necessary elements to the target audience of Web systems developers.


#g


------------
Graham Klyne
(GK@ACM.ORG)
Received on Tuesday, 3 April 2001 06:41:50 GMT

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