code: public Map<String, Set<String>> queriesForIds(Collection<String> ids) {
          Set<String> idsWithParents = getIdsForIdsWithAncestors(ids);
          Map<String, Set<String>> queries = new HashMap<String, Set<String>>();
          for (String id : idsWithParents) {
              queries.put(id, getIdsForIdWithDescendants(id));
          }
          return queries;
      }
docs: Given a set of seed IDs, expand that set of IDs to include all ancestor
  IDs, then return a map from each ID in the set to the descendant IDs
  (including the ID itself).
  
  @param ids
  The seed IDs.
  @return The mapping.