new (POSTed) annotation:
ns rdf=<http://www.w3.org/1999/02/22-rdf-syntax-ns#>
ns a=<http://www.w3.org/2000/10/annotation-ns#>
ns t=<http://www.w3.org/2001/03/thread#>
ask (?annotation rdf:type a:Annotation.
?annotation a:annotates ?annotates.
?annotation a:context ?context.
?annotation a:body ?body)
collect (?annotation ?body)