From: Dan Connolly (connolly@w3.org)
Date: 01/04/01
Tim Berners-Lee wrote:
>
> My questions about the DAML+OIL spec as revised may be based on ignorance of
> meetings I wasn't at, in which case I apologize - please accept them as
> clarification questions.
>
[...]
> 2. sameClassAs and equivalentTo; same comment as 1except for domain and
> range constraints.
This needs to be written up as a case-study in evolution... lemme
sketch it out:
An RDFS agent knows these two rules:
A
{
:s :specl :o.
:specl rdfs:subPropertyOf :genl.
} log:implies {
:s :genl :o.
}
B
{
:x rdf:type :sub.
:sub rdfs:subClassOf :super.
} log:implies {
:x rdf:type :super.
}
but it doesn't know anything about daml:equivalentTo.
and daml+ont.daml says
daml:sameClassAs rdfs:subPropertyOf rdfs:subClassOf.
Thus, when an RDFS(-only) agent is presented with
:Dog daml:sameClassAs :Canine.
:sparky rdf:type :Dog.
it can conclude
:Dog rdfs:subClassOf :Canine.
and hence
:sparky rdf:type :Canine.
Unfortunately, in order to get and RDFS-only agent to infer
:lassie rdf:type :Dog.
from
:lassie rdf:type :Canine.
it must also be told
:Canine daml:sameClassAs :Dog.
which is redundant for DAML agents.
[...]
> Are we suggesting
> that ontology builders in turn should define "sameCarAs" and "sameVehicleAs"
> properties?
No, I don't think so; There's no W3C recommendation regarding
cars that we feel obliged to support.
> This is the example being set. I found that when converting
> between different syntaxes, one has to introduce daml:equivalentTo as part
> of that translation, because different syntaxes have different abilties to
> map a graph into a tree. I missed it being defined by rdfs and now I see it
> has slipped out of daml.
er... huh? I'm not aware of any decision to get rid of
daml:equivalentTo.
It's there:
<Property ID="equivalentTo">
-- http://www.daml.org/2000/12/daml+oil.daml
$Id: daml+oil.daml,v 1.2 2001/01/02 19:15:55 mdean Exp $
and:
<equivalentTo,?C,?D> IC(?C) = IC(?D)
-- http://www.daml.org/2000/12/semantics.html
Wed, 03 Jan 2001 18:45:23 GMT
$Revision: 1.2 $ of $Date: 2001/01/02 18:56:02 $
Hmm.. it's not used in
http://www.daml.org/2000/12/daml+oil-ex.daml
nor mentioned in
http://www.daml.org/2000/12/daml+oil-walkthru.html
and I don't see it in "Appendix One: List of all language elements"
of http://www.daml.org/2000/12/reference.html
$Revision: 1.1 $ of $Date: 2001/01/03 18:38:43 $
So yes, it does seem to be slipping out. Frank, please document
it in the reference; i.e. in anything that claims
to be exhaustive; and if you get a chance, in the walkthru.
--
Dan Connolly, W3C http://www.w3.org/People/Connolly/
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