code: def _normalize_issue_dir_with_dtd(self, path):
          
          if exists(join(path, 'resolved_issue.xml')):
              return
          issue_xml_content = open(join(path, 'issue.xml')).read()
          sis = ['si510.dtd', 'si520.dtd', 'si540.dtd']
          tmp_extracted = 0
          for si in sis:
              if si in issue_xml_content:
                  self._extract_correct_dtd_package(si.split('.')[0], path)
                  tmp_extracted = 1
  
          if not tmp_extracted:
              message = "It looks like the path " + path
              message += " does not contain an si510, si520 or si540 in issue.xml file"
              self.logger.error(message)
              raise ValueError(message)
          command = ["xmllint", "--format", "--loaddtd",
                     join(path, 'issue.xml'),
                     "--output", join(path, 'resolved_issue.xml')]
          dummy, dummy, cmd_err = run_shell_command(command)
          if cmd_err:
              message = "Error in cleaning %s: %s" % (
                  join(path, 'issue.xml'), cmd_err)
              self.logger.error(message)
              raise ValueError(message)
docs: issue.xml from Elsevier assume the existence of a local DTD.
          This procedure install the DTDs next to the issue.xml file
          and normalize it using xmllint in order to resolve all namespaces
          and references.