anchor.diff:  |==========================================
   1.  Classes
   +
  -If there is GRAPH clause being applied, we retrieve a list of classes using a query described in Listing
  +we retrieve a list of classes using a query described in Listing
   <<query_for_classes_on_a_graph, 5>> and
  -<<query_for_classes_having_instances_on_a_graph, 6>>.
  +<<query_for_classes_having_instances_on_a_graph, 6>> if there is GRAPH clause being applied;
  +otherwise
  +Listing <<query_for_classes_on_background_graph, 7>> and
  +<<query_for_classes_having_instances_on_background_graph, 8>>.
   +
   [[query_for_classes_on_a_graph]]
   .Listing 5. Obtain the classes on a graph g
  
positive.code: [start=2]
  . Use HTTP URIs so that people can look up those names
  +
  We assume all subjects of statements are things. If there is GRAPH clause being applied, we search invalid
  statement using a query described in Listing
  <<non_http_uri_subject_on_a_graph, 15>>, and if nothing is found the endpoint
  satisfied this rule.
  +
  Note that we ignore Virtuoso specific graphs since Virtuoso contains a
  
negative.code: ....
  4.  Properties
  +
  We retrieve a list of properties using a query described in Listing
  <<query_for_properties_on_a_graph, 13>> if there is GRAPH clause being applied;
  otherwise Listing
  <<query_for_properties_on_background_graph, 14>>.
  +
  [[query_for_properties_on_a_graph]]
  .Listing 13. Obtain the properties on a graph g
  