code: @Override
      public Set<RelationID> getReferredTables(QuotedIDFactory idfac) {
          Set<RelationID> referredTables = new HashSet<>();
  
          for (String[] fk : fks) {
              RelationID pkTableId = getRelationIDFromString(fk[2], idfac);
              referredTables.add(pkTableId);
          }
  
          return referredTables;
      }
docs: Extracts relation IDs for all relations referred to by the user supplied foreign keys
  (but not the relations of the foreign keys)
  
  @param idfac QuotedIDFactory
  @return relation ids that are referred to by foreign keys