EasyRDF: how to create a blank node and set a rdf:about property?

I am using EasyRdf to create a few nodes in the graph. My problem is that I am trying to create a new blank node and also set an rdf:about property to it that points to the correct resource.

$rdf = new EasyRdf_Graph(); 

$datapoint_resource = $rdf->newBNode(
    'rdf:Description'
);

The problem with this code is that it creates a new rdf:Description node but there's no way I can add rdf:about as a property to it.

<rdf:Description>
    <!-- Some resources here -->
</rdf:Description>

What I need is

<rdf:Description rdf:about="http://link.to/my/resource/id">
    <!-- Some resources here -->
</rdf:Description>

I've tried adding rdf:about as a resource but the W3C validator outputs the error "rdf:about is not allowed as an element tag here".

   <rdf:Description>
     <rdf:about rdf:resource="http://ordex.probook/rdf/datapoint/5813af3dbf552b25ed30fd5c9f1eea0b"/>
   </rdf:Description>

So this doesn't work and it probably isn't a good idea either.

How can I add rdf:about when creating a new blank node or what other things do you suggest?

Solution

rdf:about is used in the RDF/XML serialization of an RDF graph to indicate the URI of a resource. Blank nodes, which you're creating with Graph.newBNode() don't have URIs. To create a URI resource, you Graph.resource(uri). Thus, you should do this instead:

$datapoint_resource = $rdf->resource('http://link.to/my/resource/id');

For more about how rdf:about is used; see the RDF 1.1 XML Syntax. It includes, for instance, this example:

The Figure 2 graph consists of some nodes that are IRIs (and others that are not) and this can be added to the RDF/XML using the rdf:about attribute on node elements to give the result in Example 2:
EXAMPLE 2 Node Elements with IRIs added
<rdf:Description rdf:about="http://www.w3.org/TR/rdf-syntax-grammar">
  <ex:editor>
    <rdf:Description>
      <ex:homePage>
        <rdf:Description rdf:about="http://purl.org/net/dajobe/">
        </rdf:Description>
      </ex:homePage>
    </rdf:Description>
  </ex:editor>
</rdf:Description>