code: public String header(Engine engine) {
          List<String> result = new LinkedList<String>();
          if (exportInputValues) {
              for (InputVariable inputVariable : engine.getInputVariables()) {
                  result.add(inputVariable.getName());
              }
          }
          if (exportOutputValues) {
              for (OutputVariable outputVariable : engine.getOutputVariables()) {
                  result.add(outputVariable.getName());
              }
          }
          return Op.join(result, separator);
      }
docs: Gets the header of the dataset for the given engine
  
  @param engine is the engine to be exported
  @return the header of the dataset for the given engine