W3C home > Mailing lists > Public > public-wai-ert@w3.org > December 2007

use of owl:cardinality?

From: Yoshio Fukushige <fukushige.yoshio@jp.panasonic.com>
Date: Mon, 17 Dec 2007 16:29:15 +0000
To: public-wai-ert@w3.org
Cc: fukushige.yoshio@jp.panasonic.com
Message-Id: <20071218004559.2156.FUKUSHIGE.YOSHIO@jp.panasonic.com>




Dear group,

I read the Las Call Working Draft of the Evaluation and Report Language
(EARL) 1.0 Schema[1], and might have found an issue in the EARL 1.0 Schema in RDF/XML
in Appendix A.

My concern in brief: Use of owl:cardinality would be better than having
min and max cardinality restrictions

(I checked the issues document, but could not find a relevant
description)

In the schema, one can find descriptions like following:

---
<owl:Restriction>
        <owl:onProperty rdf:resource="http://www.w3.org/ns/earl#assertedBy"/>
        <owl:minCardinality rdf:datatype="http://www.w3.org/2001/XMLSchema#nonNegativeInteger">1</owl:minCardinality>
        <owl:maxCardinality rdf:datatype="http://www.w3.org/2001/XMLSchema#nonNegativeInteger">1</owl:maxCardinality>
</owl:Restriction>
---

I wonder why you don't use owl:cardinality if you want to specify the
exact cardinality.

And I'm wondering if descriptions like above are invalid against the OWL
Reference document[2].

In 3.1.2 Property restrictions [3], the reference says:

---------------
Property restrictions have the following general form:

<owl:Restriction>
  <owl:onProperty rdf:resource="(some property)" />
  (precisely one value or cardinality constraint, see below)
</owl:Restriction>

The class owl:Restriction is defined as a subclass of owl:Class. A restriction class should have exactly one triple linking the restriction to a particular property, using the owl:onProperty property. The restriction class should also have exactly one triple that represents the value constraint c.q. cardinality constraint on the property under consideration, e.g., that the cardinality of the property is exactly 1. 

Property restrictions can be applied both to datatype properties (properties for which the value is a data literal) and object properties (properties for which the value is an individual). For more information about this distinction, see the section on properties. 
-------------

I don't understand the meaning of "c.q", but it seems that one cannot
put multiple triples representing value/cardinality constraints in the
description of (an anonymous Class) Restriction.

It's OK, I guess, if you just say like:

<owl:Class about="#someClass">
 <rdfs:subClassOf>
  <owl:Restriction>
        <owl:onProperty rdf:resource="http://www.w3.org/ns/earl#assertedBy"/>
        <owl:minCardinality rdf:datatype="http://www.w3.org/2001/XMLSchema#nonNegativeInteger">1</owl:minCardinality>
  </owl:Restriction>
 </rdfs:subClassOf>
 <rdfs:subClassOf>
  <owl:Restriction>
        <owl:onProperty rdf:resource="http://www.w3.org/ns/earl#assertedBy"/>
        <owl:maxCardinality rdf:datatype="http://www.w3.org/2001/XMLSchema#nonNegativeInteger">1</owl:maxCardinality>
  </owl:Restriction>
 </rdfs:sbClassOf>
</owl:Class>

but, if the cardinality should exactly specified, the use of
owl:cardinality would be better for simplicity.

Best,
Yoshio Fukushige 

[1] http://www.w3.org/TR/EARL10-Schema/#schema-rdf
[2] http://www.w3.org/TR/owl-ref
[3] http://www.w3.org/TR/owl-ref/#Restriction
-- 
Yoshio Fukushige <fukushige.yoshio@jp.panasonic.com>
Network Development Center,
Matsushita Electric Industrial Co., Ltd.
Received on Monday, 17 December 2007 16:44:16 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Tuesday, 8 January 2008 14:18:29 GMT