def retrieve_code_system_for_model
      code_system = attr_val("#{@code_list_xpath}/@codeSystem")
      if code_system
        code_system_name = HQMF::Util::CodeSystemHelper.code_system_for(code_system)
      else
        code_system_name = attr_val("#{@code_list_xpath}/@codeSystemName")
      end
      code_value = attr_val("#{@code_list_xpath}/@code")
      { code_system_name => [code_value] } if code_system_name && code_value
    end
def retrieve_code_system_for_model
      code_system = attr_val("#{@code_list_xpath}/@codeSystem")
      if code_system
        code_system_name = HQMF::Util::CodeSystemHelper.code_system_for(code_system)
      else
        code_system_name = attr_val("#{@code_list_xpath}/@codeSystemName")
      end
      code_value = attr_val("#{@code_list_xpath}/@code")
      { code_system_name => [code_value] } if code_system_name && code_value
    end
Extract the code system from the xml taht the document should use