W3C home > Mailing lists > Public > www-rdf-interest@w3.org > February 2000

Re: assymetric reference of properties

From: martin <martin@csi.forth.gr>
Date: Tue, 01 Feb 2000 14:06:57 +0200
Message-ID: <3896CC61.5D16B64E@ics.forth.gr>
To: Eric Hellman <eric@openly.com>
CC: Jeff Sussna <jeff.sussna@quokka.com>, www-rdf-interest@w3.org


Eric Hellman wrote:
> 
> At 9:04 AM -0800 1/28/00, Jeff Sussna wrote:
> >Seems like there might be another solution. This solution begins to step
> >away from "orthodox" RDF and points to taking first-class properties
> >seriously. It involves making the property an object in its own right. In
> >other words, rather than saying "x is identified by y" and "y identifies x",
> >one would say something along the lines of
> >"instance-of-identification-property connects x and y".
> 
> And in fact, that's exactly what we did, but we still wanted to have
> reciprocal properties between the link object and the node objects.
> 
> I like martin's idea of having a single property name for both
> directions. I think you can do it with the current RDFS, although
> when you have multiple range and domain classes you get less
> validation.
> 
> Eric

Dear Eric, Jeff,

Actually the TELOS Language we use to work with deals properties and
property
instances as objects in their own right. In contrast to Description
Logic, where
a Role instance is uniquely identified by x, y, and the Role type, in
TELOS you
may connect two class instances x, y with more than one instance of the
same 
property, e.g. in order to express different opinions. But also
hierarchies of
property types cause occurrence of multiple instances of the same
property 
between the same class instances: The difference may be in the subtype,
one 
is instance of another subproperty than the other. Further, one can
assign
properties to properties:

E.g.: Action "carried_out_by" Actor may have a property "in the role of"
       and/ or a property "source" (denoting where the knowledge about
this
       property instance comes from)

In any case I think dealing with property instances as full objects is
by far
clearer and removes an unnecessary assymetry between classes and
properties.

I have not understood why Eric says we may have less validation. I have
not
actually proposed not to distinguish the direction of a property
instance
with respect to domain and range. Some properties are symmetric, but
most
are directed, and the name of a directed property expresses the
direction.
Hence a declaration of a property instance should refer to the direction
of instantiation in the one or the other way. Inverse use could be
indicated

- by an RDFS statement identifying two properties as inverse of each
other
   and using the respective property,
- or by a syntactic element declaring a property instantiation as
inverse use,
- or by declaring a property instance explicitly from the domain
instance to the range instance
    in a descripription of the range instance,
- or by using one of a tuple of two names per property, 

where I like the last more than the first.

Martin



> 
> >
> >Jeff
> >
> >-----Original Message-----
> >From: Eric Hellman [mailto:eric@openly.com]
> >Sent: Thursday, January 27, 2000 7:46 PM
> >To: martin; www-rdf-interest@w3.org
> >Subject: Re: assymetric reference of properties
> >
> >
> >We encountered the same situation in our linking metadata schema. A
> >lot of code was expended making sure that we don't get stuck in
> >endless loops while traversing models with these reciprocal
> >relationships- probably its a good excuse to keep the "inverse"
> >property out of rdfs. But I certainly agree that it's a needed
> >facility at some level.
> >
> >Eric
> 
> Eric Hellman
> Openly Informatics, Inc.
> http://www.openly.com/           21st Century Information Infrastructure
> LinkBaton: Your Shortcuts to Information  http://linkbaton.com/

-- 

--------------------------------------------------------------
 Dr. Martin Doerr              |  Vox:+30(81)391625          |
 Senior Researcher             |  Fax:+30(81)391609          |
 Project Leader SIS            |  Email: martin@ics.forth.gr |
                                                             |
  Centre for Cultural Informatics and Documentation Systems  |
                Institute of Computer Science                |
   Foundation for Research and Technology - Hellas (FORTH)   |
                                                             |
 Vassilika Vouton,P.O.Box1385,GR71110 Heraklion,Crete,Greece |
                                                             |
  Web-site: http://www.ics.forth.gr/proj/isst/index.html     |
--------------------------------------------------------------
Received on Tuesday, 1 February 2000 07:02:20 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Monday, 7 December 2009 10:51:42 GMT