public String toString() {
		String s = "RDFNode {";
		if( subjectUri != null ) s += "\n  subjectUri = "+subjectUri;
		if( sourceUri != null  ) s += "\n sourceUri = "+sourceUri;
		if( simpleValue != null ) s += "\n  simpleValue = "+simpleValue;
		for( Map.Entry<String,Set<RDFNode>> prop : properties.entrySet() ) {
			for( RDFNode v : prop.getValue() ) {
				s += "\n  "+prop.getKey()+" = "+v.toString().replace("\n", "\n  ");
			}
		}
		if( s.length() > 9 ) s += "\n";
		s += "}";
		return s;
	}