code: public Map<String, Set<DataUsage>> getDataUsageFor(String activity) throws CompatibilityException {
                  validateActivity(activity);
                  if (activityDataUsage.get(activity) == null) {
                          return new HashMap<>(); //No input data elements for this activity
                  }
                  return Collections.unmodifiableMap(activityDataUsage.get(activity));
          }
docs: Returns all attributes of the given activity together with their
  usage.<br>
  If the given attribute has no attributes, the returned set contains
  no elements.<br>
  The given activity has to be known by the context, i.e. be contained
  in the activity list.
  
  @param activity Activity for which the attribute usage is requested.
  @return All attributes of the given activity together with their
  usage.
  @throws ParameterException
  @throws CompatibilityException
  @throws IllegalArgumentException IllegalArgumentException If the
  given activity is not known.
  @see #getActivities()