W3C home > Mailing lists > Public > www-webont-wg@w3.org > March 2002

comments on OWL-lite: meaning of 'required' values

From: Dan Brickley <danbri@w3.org>
Date: Tue, 26 Mar 2002 09:50:02 -0500 (EST)
To: <www-webont-wg@w3.org>
Message-ID: <Pine.LNX.4.30.0203260933390.16087-100000@tux.w3.org>

A couple of comments.

http://www.cs.vu.nl/~frankh/spool/OWL-first-proposal/motivation.html#core
[[
The frame portion of the definitions captures the widely understood frame idiom.

Each frame-idiom class-definition contains
	a collection of super-classes and
	a collection of property definitions, in the form of the slot construct.
	The slot construct states the local range of a property,
	whether a value is optional or required,
...
]]

There are a couple of ways in which 'required' might be understood.

In XML-based schema languages, "required" is often "required to be
present in some XML document / description". Others use "required" in the
sense of "it isn't a member of class Foo unless it has a value for the
'bar' property".

For example an XML schema-like approach might require that each concrete
description of a member of the class eg:Person includes a value for their
eg:biologicalParent property.  This is different to saying something
like "all people have parents", since the latter doesn't care about the
content of specific XML instances that describe people. Implementors seem
to want both.

This is one of the cultural mismatches between some of the XML and RDF
work, so might be worth adding some clarifying text to the OWL-Lite
overview.

One other comment re

"Individuals - can be given names or can be anonymous"

This wording suggests that nameless-ness is an intrinsic characteristic of
the individual, rather than a characteristic of some description of that
individual. Two XML documents might partially describe the same
individual; one description might mention a URI name while the other
mightn't. Saying "individuals can be... anonymous" encourages the
expectation that there is a class of nameless individuals.

cheers,

Dan
Received on Tuesday, 26 March 2002 09:50:02 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Monday, 7 December 2009 10:57:48 GMT