using datatype for ObjectProperty range

I have declared the following class and its property in OWL.

 

<!-- Open class. Category : Open -->

 <owl:Class rdf:ID="Open" rdfs:label="Open">

 <rdfs:comment>A category of unrestricted data or public
data</rdfs:comment> 

 <rdfs:subClassOf
rdf:resource="http://www.public.asu.edu/~pnivargi/ppm/ontologies/Data.ow
l#Category" /> 

 </owl:Class>

 

<!-- level property: Assigns a number as a level to each category -->

 <owl:ObjectProperty rdf:ID="level" rdfs:label="level">

 <rdfs:domain
rdf:resource="http://www.public.asu.edu/~pnivargi/ppm/ontologies/Data.ow
l#Category" /> 

 <rdfs:range
rdf:resource="http://www.w3.org/2001/XMLSchema#positiveInteger"/>

 </owl:ObjectProperty>

 

When I tested my ontology using the OWL validator provided by BBN
Technologies on 

http://owl.bbn.com/validator/

 

I get the following warnings:

 

http://www.public.asu.edu/~pnivargi/ppm/ontologies/Data.owl#level
<http://www.daml.org/cgi-bin/hyperdaml?http://www.public.asu.edu/%7Epniv
argi/ppm/ontologies/Data.owl#level> 
http://www.w3.org/2000/01/rdf-schema#range
<http://www.daml.org/cgi-bin/hyperdaml?http://www.w3.org/2000/01/rdf-sch
ema#range> 
http://www.w3.org/2001/XMLSchema#positiveInteger
<http://www.daml.org/cgi-bin/hyperdaml?http://www.w3.org/2001/XMLSchema#
positiveInteger> 

 

 

Statement Indication

 

The range restriction for an ObjectProperty can not be a datatype.

 

 

I used this because I saw this being used in an example on the OWL
specifications on w3c website. Is this not allowed? Is there any
workaround for it?

 

Prajakta