defining the range

Hi,
 I have the following ontology:

<?xml version="1.0"?>
<rdf:RDF
    xmlns="http://www.bpeng.com/ontology/2004/12/12#"
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
    xmlns:owl="http://www.w3.org/2002/07/owl#"
  xml:base="http://www.bpeng.com/ontology/2004/12/12">
  <owl:Ontology rdf:about=""/>
  <owl:Class rdf:ID="Object"/>
  <owl:Class rdf:ID="Modifier"/>
    <owl:ObjectProperty rdf:ID="modifies">
    <rdfs:domain rdf:resource="#Modifier"/>
  </owl:ObjectProperty>
  <owl:ObjectProperty rdf:ID="hasModifier">
    <rdfs:range rdf:resource="#Modifier"/>
    <rdfs:domain rdf:resource="#Object"/>
  </owl:ObjectProperty>
  <owl:DatatypeProperty rdf:about="#oid">
    <rdf:type
rdf:resource="http://www.w3.org/2002/07/owl#FunctionalProperty"/>
    <rdfs:domain rdf:resource="#IdentifiableObject"/>
    <rdfs:range rdf:resource="http://www.w3.org/2001/XMLSchema#ID"/>
    <rdfs:comment rdf:datatype="http://www.w3.org/2001/XMLSchema#string"
    >Unique object identifier</rdfs:comment>
  </owl:DatatypeProperty>
  <owl:DatatypeProperty rdf:ID="prop1">
    <rdfs:domain rdf:resource="#Object"/>
    <rdfs:range rdf:resource="http://www.w3.org/2001/XMLSchema#string"/>
  </owl:DatatypeProperty>
  <owl:DatatypeProperty rdf:ID="prop2">
    <rdfs:domain rdf:resource="#Object"/>
    <rdfs:range rdf:resource="http://www.w3.org/2001/XMLSchema#string"/>
  </owl:DatatypeProperty>
</rdf:RDF>

and I would like to specify that the property "modifies" of the class
"Modifier" has as range any property  ids  of the class "Object".

In other words if I have:

<Object ....>
    <prop1 ...>test1</prop1>
    <prop2 ...>test2</prop2>
    <hasModifier id="m1#"/>
</Object>  

<Modifier id="m1">
    <modifies .....>id of either test1, test2 or hasModifier </modifies>
</Modifier>

Any help would me much appreciated.

Thanks

Alessandro