PREFIX BASE: <http://schemas.ogf.org/nml/2013/05/base#>
PREFIX ndl-topology-owl: <http://cinegrid.uvalight.nl/owl/ndl-topology.owl#>
PREFIX sdndl: <http://www.gsi.dit.upm.es/ontologies/sdndl#>
PREFIX sdndlcao: <http://www.ctb.upm.es/ontologies/sdndlcao#>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>

SELECT DISTINCT STR(?mac_address) AS ?mac_address
                STR(?snapshot_id) AS ?snapshot_id
WHERE
{
     ?device_instance sdndlcao:deviceOfSnapshot ?snapshot_instance;
                      sdndl:hardwareAddress ?mac_address.
     ?snapshot_instance sdndlcao:snapshotId ?snapshot_id.

       {
           SELECT DISTINCT ?device_instance
                           (COUNT(?device_instance) AS ?num_snapshots)
           WHERE {
                  ?device_instance a ndl-topology-owl:Device;
                                   sdndlcao:deviceOfSnapshot ?snapshot_instance.
                 }
           GROUP BY ?device_instance
       }
      FILTER (?num_snapshots > 1)
}