code: public Set<String> getSourceNames() {
          return Sets.newHashSet(Iterables.transform(getDatasources().values(), new Function<Datasource, String>() {
  
              @Override
              public String apply(Datasource input) {
                  return input.getSource();
              }
          }));
      }
docs: Returns the set of unique source names; The names of the underlying samples used as the
  source of aggregations.
  
  @return source names