W3C home > Mailing lists > Public > public-rif-wg@w3.org > January 2007

RE: Outcomes from Jan 2 telecon

From: Gerd Wagner <wagnerg@tu-cottbus.de>
Date: Wed, 3 Jan 2007 17:11:26 +0100
To: "'Chris Welty'" <cawelty@gmail.com>, "'Public-Rif-Wg \(E-mail\)'" <public-rif-wg@w3.org>
Message-ID: <000001c72f51$d2a9fa80$14b2a8c0@informatik.tucottbus.de>

> Dave Reynolds wrote:
> > Then there was discussion on which, if any, of those three 
> should go in 
> > the core. Gerd suggested that rather than have all three in 
> the core we 
> > pick one based on use cases, I thought that received fairly broad 
> > agreement.
> 
> That wasn't my impression.  The core should, from a design 
> perspective, remain a core. The agreement I heard was that we should 
> attempt to find a way to translate between the different approaches. 
> If they are interchangeable, then it makes sense to pick one.

It also makes sense to pick just one if there is one that
covers 80% of the use cases (or languages in use).

The most basic meaning of a slot is the one used in UML 
where a "slot relates an instance specification, a structural 
feature, and a value or values. It represents that an entity 
modeled by the instance specification has a structural 
feature with the specified value or values. The values 
in a slot must conform to the defining feature of the 
slot (in type, multiplicity, etc.)."
[UML Infrastructure OMG spec document]

A UML instance specification corresponds to an RDF description
(or to an OWL individual axiom, or F-Logic ground molecule).
In a more ordinary language, we could also call it an "object 
description fact". So, a slot in this basic sense is a 
property-value pair as part of such a fact statement, which
always involves an object name (such as an OID or URIref) 
as an identifier of the object described. 

Now, in order to have slots also in queries, it is natural to 
turn object description facts into "object description atoms"
where 

1) the object name is replaced by an object term
2) the property-value pair syntax is generalized to a 
   property-term pair syntax 

and where the terms can contain free variables, as usual, 
for retrieving answers.

I claim that this is the most common usage of slots, which
we also find in OO rule languages such as Jboss rules and
IRL.

>> Justifying slotted syntax based on RDF makes little sense to me 

But there is a clear sense of slots in RDF descriptions. 
Consider, e.g., the following description (in some fictitious
RDF syntax):

description about=RIF
  type=W3C-WorkingGroup
  startdate=2005
  chairs={CW,CSMA}
  progress=slow

> I don't know where that requirement came from, I found it odd when I 
> first read it, too, but note that RDF does NOT have a relational 
> semantics. 

Sure, but the concept of slots does not depend on relational semantics.
And it's clear (I hope not only to me) that the OO/(RD)F-Logic concept 
of slots is more important to RIF that the relational one.

-Gerd
Received on Wednesday, 3 January 2007 16:21:05 GMT

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