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RE: rdfs:Property rdfs:range questions

From: Jon Hanna <jon@spin.ie>
Date: Fri, 20 Sep 2002 12:13:50 +0100
To: <www-rdf-interest@w3.org>
Message-ID: <NDBBLCBLIMDOPKMOPHLHEENOEGAA.jon@spin.ie>

> * Can someone please point to what a property range defaults to?

By default the range of a property is the set which contains all resources
and all literals (and null?).

> * IF I am correct, when a property has multiple ranges, all of them must
> be satisfied (does not make sence to me;-). Can someone please explain
> the reasons behind this?

It's partly because you can take any triple from an asserted graph and
consider them asserted. Hence if you have one triple saying a range is
<blah:image> and another saying a range is <blah:file> then you have to be
able to assert either of those triples in ignorance of the other. This is
only possible if both are satisfied.

> * How can I have two dissjoint ranges in the same property?

A resource can be of more than one class, either because it satisfies the
requirements of both classes (an image file satisfies a class for images, a
class for files, a class for objects for which a representation is
available, a class for "document" in its looser sense, etc. it could even
match some classes that describe textual resources, if those classes are
defined to include text transmitted in image form), or because of two
classes being the same or similar concept in different vocabularies
(something of type <rss:image> is also of type <dctype:Image>).

There are two ways of using range as I see it. One is in a validation role
"This predicate has a range of <dctype:Image>. The object is not asserted to
be of class <dctype:Image>, hence I detect an error.", or in an
information-generating role "This predicate has a range of <dctype:Image>,
hence the object is of class <dctype:Image> whether that is asserted or
not."
Received on Friday, 20 September 2002 07:10:24 GMT

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