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

Every property is a Class

From: Jonas Liljegren <jonas@rit.se>
Date: 20 Oct 2000 21:47:13 +0200
To: Graham Klyne <GK@dial.pipex.com>
Cc: Seth Russell <seth@robustai.net>, RDF interest group <www-rdf-interest@w3.org>
Message-ID: <87bswfwb0e.fsf_-_@jonas.rit.se>
Graham Klyne <GK@dial.pipex.com> writes:

>    [MyCar] --Model--> [FordEscort]
> I want to treat [FordEscort] as a resource that has various properties
> that describe that model of car, and, by reference, to have those
> properties apply to my car.
> Maybe [FordEscort] should be an rdf:Class?  I'm not quite comfortable
> with the idea that the model may be a class (hence object of rdf:type)
> and also an "ordinary" resource in its own right with lots of
> properties relating to some physical entity.

I feel that there is no difference between classes and properties.
Every property can be a class.

>    [MyCar] --Model--> [FordEscort]

[MyCar] --type--> [ModelFordEscort] --subClassOf--> [Model]

>    [TheBody] ----colour----> "Red"

[TheBody] --type--> [ColourRed] --subClassOf--> [Colour]

>    [TheEngine] --capacity--> "1600"

[TheEngine] --type--> [Capacity1600] --subClassOf--> [Capacity]

>    [TheEngine] --needs---->[repair]

[TheEngine] --type--> [NeedsRepair] --subClassOf--> [Needs]

Think about it.  Every property can be used to create the set of all
resoruces that have the property.  

If the engine needs repair, it's a member of the class of all things
that needs something.  We uses classes to provide a template for the

We can use the words 'is' or 'has' in place of 'type'.  MyCar is
ModelFordEscort.  TheBody has ColourRed.  TheEngine has Capacity1600.
TheEngine NeedsRepair. (Need seems to be a basic type of type, on the
level of 'is' and 'has'.)

The 'is' often indicates that we want to create a class.  The 'has'
indicates that we don't think of the property as a class.  But that
distinction has more to do with language than logic.

TheBody has ColourRed.  This means that TheBody is a member of the set
of all things with the ColourRed. And that is a subset of all things
with a Colour.  Since Colour is a class, we can describe which
properties we expect the members to have. We can say that all things
with colour must have a degree of luminocity.  We can also say things
about the set; "There are two things that has the ColourRed".  And we
can say things about the proprty defining the set.

/ Jonas Liljegren

The Wraf project http://www.uxn.nu/wraf/
Sponsored by http://www.rit.se/
Received on Friday, 20 October 2000 15:42:29 UTC

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