Trying to count the properties used for each class

[Bob DuCharme]

Using arq and the data at 
http://www.snee.com/bobdc.blog/files/BeatlesMusicians.ttl, I’m trying to 
write a query that will list the classes used in the data and the number 
of distinct properties used by instances of that class. I’m having a 
hard time and can’t even write a query that lists the number of 
properties used for just one of the classes; the following just shows me 
a series of ones.

   SELECT (COUNT(DISTINCT ?p) AS ?pcount)
   WHERE {
      ?s a <http://learningsparql.com/ns/schema/Song> .
      ?s ?p ?o .
   }
   GROUP BY ?p
Any suggestions?

Thanks,

Bob