System.Data.DataSet.ReadXml C# (CSharp) Method

        public XmlReadMode ReadXml(string fileName, XmlReadMode mode)
        {
            XmlTextReader xr = null;
            if (mode == XmlReadMode.Fragment)
            {
                FileStream stream = new FileStream(fileName, FileMode.Open);
                xr = new XmlTextReader(stream, XmlNodeType.Element, null);
            }
            else
            {
                xr = new XmlTextReader(fileName);
            }

            // Prevent Dtd entity in dataset             
            xr.XmlResolver = null;

            try
            {
                return ReadXml(xr, mode, false);
            }
            finally
            {
                xr.Close();
            }
        }

        protected void Page_Load(object sender, EventArgs e)
        {
            DataSet ds = new DataSet();
            DataSet ds1 = new DataSet();
            ds.ReadXml(@"D:\Books.xml");

            bookgrd.DataSource = ds.Tables[0];
            bookgrd.DataBind();

            IEnumerable<DataRow> tbl1row = ds.Tables[0].AsEnumerable();
            ds1.ReadXml(@"D:\Books2.xml");

            IEnumerable<DataRow> tbl2row = ds1.Tables[0].AsEnumerable();
            GridView1.DataSource = ds1.Tables[0];
            GridView1.DataBind();

            var items = tbl2row.AsEnumerable().Select(r => r.Field<string>("id"))
            .Except(tbl1row.AsEnumerable().Select(r => r.Field<string>("id")));

            DataTable TableC = (from row in tbl2row.AsEnumerable()
                                join id in items
                                on row.Field<string>("id") equals id
                                select row).CopyToDataTable();

            GridView2.DataSource = TableC;
            GridView2.DataBind();
        }