code: protected String expandSystemId(String baseId, String systemId) {
          if (baseId == null || baseId.isEmpty()) return systemId;
          if (systemId == null || systemId.isEmpty()) return baseId;
          try {
              return new URI(baseId).resolve(new URI(systemId)).toASCIIString();
      //        
      //        int lastSep = baseId.lastIndexOf('/');
      //        return baseId.substring(0, lastSep+1) + systemId;
      //        return baseId.substring(0, lastSep+1) + systemId;
          } catch (URISyntaxException ex) {
              throw new ResolvingException(toString(), ex);
          }
      }
docs: Calculates the schema file location.
  @param baseId
  @param systemId
  @return schema file path