RDF Schema design pb: inheritance of properties (XML)

Leigh Dodds ldodds at INGENTA.COM
Wed Dec 1 09:36:58 CET 1999

> But there is an inheritance hierarchy that I don't know how to handle
> using W3C's specifications alone. A genus has properties values
> (e. g. flower/petals/color = 'white' ) that MUST be inherited by the
> species in this genus. The properties values of a genus CAN be
> overriden by some species in this genus.

I believe RDF handles this, see below.

> It seems that the "refines" property in XML Schema would bring the
> desired semantics, together with the "Schema Information Set
> Contribution: augmentations to instance information sets which follow as
> a consequence of schema-validation". But the uncomplete state of the W3C
> document makes me unshure.

Hmm, I'm not 100% sure either, but my feeling is that RDF is better
suited to this task than Schema.

As I understand things - we're looking to produce a generic schema for
capturing character data. In this case, "refines" could be used to extend
the schema to include attributes/elements from other disciplines.

RDF allows you to describe 'resources' independent of the structure
of the schema they conform to, and allows things like sub-classing.

> I don't see anything clearly specified in RDF and RDF Schema for
> inheritance of properties.

>>>From the RDF Schema spec : http://www.w3.org/TR/PR-rdf-schema/

"Classes themselves are often organised in a hierarchical fashion,
for example the class 'dog' might be considered a sub-class of 'animal'
which is a sub-class of 'organism' etc., meaning that any resource which is
of rdf:type 'dog' is ipso facto also of rdf:type 'animal' and so on. This
specification describes a property, rdfs:subClassOf, to denote such
between classes."

...and (describing subClassOf)...

"If class A is a sub-class of some broader class B, and B is a sub-class of
then A is also implicitly a sub-class of C. Consequently, resources that are
instances of class A will also be instances of C, since A is a sub-set of
both B and C"

...and (describing subPropertyOf)...

"If the property biologicalFather is a sub-property of the broader
property biologicalParent, and if Fred is the biologicalFather of John, then
it is implied that Fred is also the biologicalParent of John."

I think these portions of the spec apply to the sort of 'inheritance' you
require - or am I missing a subtle difference here? If you wish to
provide default values for properties then I think this needs to be
addressed at an application level.

> Info. for computer men: biology has a hierarchic classification of
> species whose 4 lowest levels are: order family genus species

Heres an RDF example of this structure (I've kept it to the
lower 4 levels of the classification, ignoring Kingdom, Phylum, Class,

<rdf:Description ID="Order">
<rdfs:subClassOf rdf:resource="http://www.foo.com/taxonomy-schema#Class"/>

<rdf:Description ID="Family">
<rdfs:subClassOf rdf:resource="#Order"/>

<rdf:Description ID="Genus">
<rdfs:subClassOf rdf:resource="#Family"/>

<rdf:Description ID="Species">
<rdfs:subClassOf rdf:resource="#Genus"/>

Here we can declare Chrysanthemum to be a subclass of species, forgive
me for not knowing the latin name...

<rdf:Description ID="Chrysanthemum">
<rdfs:subClassOf rdf:resource="#Species" />

However, and this is where I'm still wrestling with RDF to an extent,
there are other ways to achieve this. For example, we may not need Genus and
classes - instead modelling the Chrysanthemum genus as a class, and species
as subclasses.
Note that RDF does allow a resource to be a subclass of more than one class.

I can see a lot of work ahead in this area, and there seems to be a wealth
different ways to model the same ideas. I'm at present digging through the
literature to come up with some decent examples. (I hope the above was



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