SPTP11 — Performance Profile Loads need tags for throughput

The PAclosedLoad and PAopenLoad stereotypes should both have tags for
throughput
in [responses/unit_time]. The PAresource stereotype has already a
PAthroughput tag
of type Real, so this would be suitable.

A more appropriate type for Throughput would be desirable.

• PAperfValue is suitable for describing delay, and time between
  events, but
  not a rate.

• RTarrivalPattern type is good for describing event sequences, but
  it
  assumes that the event pattern is imposed on the system. Throughput is
  usually a
  result, and often we don't know its pattern but only the mean rate.

• A full treatment of throughput might have to treat traffic
  variability and
  self-similarity!!