xml read, write, modify data in asp.net

wsex.aspx.cs:
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Xml;

public partial class wsex : System.Web.UI.Page
{
string xmlfile = @"C:\vision\first\emp.xml";
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
getdata();
}
void getdata()
{
wsxml ws = new wsxml();
GridView1.DataSource = ws.getdata();
GridView1.DataBind();
}

protected void Button1_Click(object sender, EventArgs e)//insert
{
XmlDocument xd = new XmlDocument();
xd.Load(xmlfile);
XmlElement xe = xd.CreateElement("emp");

XmlElement id = xd.CreateElement("id");
id.InnerText = TextBox1.Text;
xe.AppendChild(id);

XmlElement nam = xd.CreateElement("name");
nam.InnerText = TextBox2.Text;
xe.AppendChild(nam);

XmlElement ad = xd.CreateElement("add");
ad.InnerText = TextBox3.Text;
xe.AppendChild(ad);

xd.DocumentElement.AppendChild(xe);
xd.Save(xmlfile);
Response.Redirect("~/wsex.aspx");

}
protected void Button2_Click(object sender, EventArgs e)//update
{
DataSet ds = new DataSet();
ds.ReadXml(Server.MapPath("emp.xml"));
for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
{
if (TextBox1.Text == ds.Tables[0].Rows[i]["id"].ToString())
{
ds.Tables[0].Rows[i]["name"] = TextBox2.Text;
ds.Tables[0].Rows[i]["add"] = TextBox3.Text;
ds.WriteXml(Server.MapPath("emp.xml"));
}
}
Response.Redirect("~/wsex.aspx");
}
protected void Button3_Click(object sender, EventArgs e)//delete
{
DataSet ds = new DataSet();
ds.ReadXml(Server.MapPath("emp.xml"));
for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
{
if (TextBox1.Text == ds.Tables[0].Rows[i]["id"].ToString())
{
ds.Tables[0].Rows[i].Delete();
ds.WriteXml(Server.MapPath("emp.xml"));
}
}
Response.Redirect("~/wsex.aspx");
}
}

emp.xml:

<?xml version="1.0" standalone="yes"?>

<employee>

  <emp>

    <id>1</id>

    <name>s</name>

    <add>s</add>

  </emp>

  <emp>

    <id>2</id>

    <name>b</name>

    <add>che</add>

  </emp>

  <emp>

    <id>3</id>

    <name>c</name>

    <add>ban</add>

  </emp>

</employee>

wsxml:(webservice class)

[WebMethod]

    public DataSet getdata()

    {

        DataSet ds = new DataSet();

        ds.ReadXml(Server.MapPath("emp.xml"));

        return ds;

    }