According to the specs (http://www.w3.org/TR/REC-rdf-syntax/#section-Syntax-ID-xml-base), rdf:ID="name" is equivalent to rdf:about="#name", both resolve to IRIs against the base IRI of the infoset.

OO jDREW associates the type referenced in

<Var type="string">X</Var>

with the type specified in

<rdf:Description rdf:ID="string">
      <rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>
    </rdf:Description>
</rdf:RDF>

This itself is incorrect, as it should be <Var type="#string">X</Var> assuming xml:base is the same in both cases.

However, the content model of @type in <Var> should be xs:anyURI, so

<Var type="http://www.w3.org/2001/XMLSchema#string">X</Var>

should reference the type defined in

<rdf:Description rdf:ID="string" xml:base="http://www.w3.org/2001/XMLSchema">
      <rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>
    </rdf:Description>
</rdf:RDF>

Instead, the error message "There is no type http://www.w3.org/2001/XMLSchema#string defined." appears.

Because rdf:ID is of type xs:ID, it is not correct to have

<rdf:Description rdf:ID="http://www.w3.org/2001/XMLSchema#string" xml:base="http://www.w3.org/2001/XMLSchema">
<rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class&quot;/>
</rdf:Description>
</rdf:RDF>

A correct alternative (valid according to RDF, RDFS specs) would be

<rdf:Description rdf:about="http://www.w3.org/2001/XMLSchema#string" >
<rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class&quot;/>
</rdf:Description>
</rdf:RDF>

but this is also not parsed by OO jDREW.

A test KB is

<RuleML  xmlns="http://ruleml.org/spec">
  <Assert>
    <Atom>
       <Rel>P</Rel>
       <Ind type="http://www.w3.org/2001/XMLSchema#string">stringParam</Ind>
   </Atom> 
  </Assert>
</RuleML>

which does not parse, compared to

<RuleML  xmlns="http://ruleml.org/spec">
  <Assert>
    <Atom>
       <Rel>P</Rel>
       <Ind>stringParam</Ind>
   </Atom> 
  </Assert>
</RuleML>

which does parse.