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typed containers in RDF Schema

From: Garret Wilson <garret@globalmentor.com>
Date: Fri, 5 Apr 2002 09:06:57 -0600
Message-ID: <005901c1dcb3$882f1c10$d8f30cd8@odysseus2001>
To: <www-rdf-comments@w3.org>
Everyone,

My name is Garret Wilson, and my company, GlobalMentor, Inc., is an
implementer of RDF. Our Mentoract Reader product, a cross-platform eBook
reading application ( http://www.globalmentor.com/software/reader/ ) will in
its next version fully support browsing any embedded RDF in eBooks and HTML
pages. I'm also the editor of XPackage ( www.xpackage.org ), an RDF-based
framework for creating packaging information that will be used as a basis of
the Open eBook Forum's OEB Publication Structure 2.0.

I was recently informed that the final version of RDF Schema will not
include support for so-called "long-range" range constraints for collection
members. This is really a shame, and it makes creating an RDF editor
difficult.

Imagine you have an RDF editor based on RDF Schema---you tell it the schemas
you want to use, and it presents the appropriate editors for each property.
For a "title" property, the editor would be a simple text field, as the
schema would indicate xsd:string as the range.

But what would we do for a "keywords" property? This should be an rdf:Bag of
related keywords, and each should be a string. Here are the options if RDF
Schema does not support typed containers:

* We could simply assume that if xsd:string is allowed, then an rdf:Bag of
xsd:strings is also allowed. (This would be an incorrect use of RDF Schema,
but it would fulfill the purpose.)

* We could assume that if an rdf:Bag and xsd:string range are *both*
allowed, then that implies that only an rdf:Bag of xsd:string is allowed.
(Again, this is incorrect usage of RDF Schema.)

* We could only allow an rdf:Bag for the property, but for values the user
would be able to enter literals, other properties, etc. This is a correct
interpretation of RDF Schema, but it isn't really acceptable, and creates a
huge inconsistency with simple strings.

This is a real problem, one that I've been trying to address recently both
in software we're implementing and in our consultations with another large
company considering implementing RDF. How can we ensure that RDF Schema will
be able to specify the specific types allowed in a container range?

Sincerely,

Garret Wilson
President, GlobalMentor, Inc.
Member, W3C, Unicode, OEBF
Received on Friday, 5 April 2002 10:07:33 GMT

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