用SqlDataAdapter更新数据库问题

        SqlConnection conn = new SqlConnection("Server=;Integrated Security=true;" + "Database=xml");
        SqlDataAdapter thisAdapter = new SqlDataAdapter("Select * from xml", conn);
        SqlCommandBuilder thisAder = new SqlCommandBuilder(thisAdapter);
        DataSet thisDataSet = new DataSet();
        thisAdapter.Fill(thisDataSet, "mydataset");
        DataRow row;
        row = mydataset.NewRow();
        row["ID"] = titleList[0].FirstChild.Value;
        row["书名"] = titleList[1].FirstChild.Value;
        row["分类号"] = titleList[2].FirstChild.Value;
        row["出版地"] = titleList[3].FirstChild.Value;
        row["出版日期"] = titleList[4].FirstChild.Value;
        row["ISBN"] = titleList[5].FirstChild.Value;
        row["页码"] = titleList[6].FirstChild.Value;
        row["内容"] = titleList[7].FirstChild.Value;
        row["正文文件"] = titleList[8].FirstChild.Value;
        mydataset.Rows.Add(row);
        thisAdapter.Update(thisDataSet, "mydataset");
        conn.Close();

 

调试时的信息是：错误 1 当前上下文中不存在名称“mydataset” 谁知道这个怎么定义呢？