rdf:property expressions in DAML

A Trivial question.

I have noticed in Process.owl and also CongoProcess.owl that certain 
properties have been expressed as rdf:property rather than 
owl:DatatypeProperty or owl:ObjectProperty, though the range is not 
owl#Thing For e.g.

rdf:Property rdf:ID="locateBookOutput">
  <rdfs:subPropertyOf 
rdf:resource="http://www.daml.org/services/owl-s/0.9/Process.owl#output" />
  <rdfs:domain rdf:resource="#LocateBook" />
  <rdfs:range rdf:resource="#LocateBookOutput" />
  </rdf:Property>

and

- <rdf:Property rdf:ID="nameBookInCatalogue">
  <owl:domain rdf:resource="#BookInCatalogue" />
  <owl:range rdf:resource="http://www.w3.org/2001/XMLSchema#string" />
  </rdf:Property>

Could there be a specific reason behind doing this or does it not matter?

Thanks,

Monika
-- 
 >**<>**<>**<>**<>**<>**<>**<>**<>**<>**<
Monika Solanki
De Montfort University
Software Technology Research Laboratory
Hawthorn building, H00.18
The Gateway.
Leicester LE1 9BH, UK

phone: +44 (0)116 250 6170 intern: 6170
email: monika@dmu.ac.uk <mailto:monika@dmu.ac.uk>
web: http://www.cse.dmu.ac.uk/~monika/ 
<http://www.cse.dmu.ac.uk/%7Emonika/>
 >**<>**<>**<>**<>**<>**<>**<>**<>**<>**<
"NOTE: The information transmitted is intended only for the person or 
entity to which it is addressed and may contain confidential and/or 
privileged material. Any review, retransmission, dissemination or other 
use of, or taking of any action in reliance upon this information by 
persons or entities other than the intended recipient is prohibited. If 
you received this in error, please contact the sender and delete the 
material from any computer"