I'm writing an OpenCMIS based application, which extracts some data from Alfresco 3.3.

It works fine with standard CMIS properties such as cmis:name or cmis:contentStreamMimeType; however, I can't access Alfresco especific properties, which are present on the CMIS AtomPub feed as "Alfresco extensions":

<cmisra:object>
  <cmis:properties>
    <cmis:propertyString propertyDefinitionId="cmis:name" displayName="Name" queryName="cmis:name">
      <cmis:value>test document</cmis:value>
    </cmis:propertyString>
    <cmis:propertyString propertyDefinitionId="cmis:contentStreamMimeType" displayName="Content Stream MIME Type" queryName="cmis:contentStreamMimeType">
      <cmis:value>text/html</cmis:value>
    </cmis:propertyString>
    ...
    <alf:aspects>
      ...
      <alf:properties>
        <cmis:propertyString propertyDefinitionId="cm:description" displayName="Description" queryName="cm:description">
          <cmis:value>This is just a test document</cmis:value>
        </cmis:propertyString>
      </alf:properties>
    </alf:aspects>
  </cmis:properties>
</cmisra:object>

Is there any way in which I can get the value of cm:descripcion, with OpenCMIS?

My guess is that I need to use the DocumentType interface instead of Document, and then call its getExtensions() method. But I don't know how to get an instance of DocumentType.

Any help would be really appreciated.

Regards

Edit: altough Florian's answer already worked out for me, I've just realized that I can get these properties' values with CMIS SQL, too:

select d.*, t.*, a.*
from   cmis:document d
join   cm:titled t on d.cmis:objectid = t.cmis:objectid
join   cm:author a on d.cmis:objectid = a.cmis:objectid
where  t.cm:description like ...