Data Relation Through DataSet

SqlConnection con=new SqlConnection (ConfigurationManager.ConnectionStrings["kumarConnectionString"].ConnectionString);

protected void Button1_Click1(object sender, EventArgs e)
{


DataSet ds = new DataSet();
string firstSql = null;

//connetionString = "Data Source=ServerName;Initial Catalog=DatabaseName;User ID=UserName;Password=Password";
firstSql = "select * from emp;";
firstSql += "select * from dep";


try
{
SqlCommand cmd = new SqlCommand(firstSql, con);
SqlDataAdapter adp = new SqlDataAdapter(cmd);
adp.Fill(ds);
//creating data relations
DataRelation relation;
DataColumn table1Column;
DataColumn table2Column;
//retrieve column
table1Column = ds.Tables[0].Columns[0];
table2Column = ds.Tables[1].Columns[0];
//relating tables
relation = new DataRelation("relation", table1Column, table2Column);
//assign relation to dataset
ds.Relations.Add(relation);
Response.Write("Data relation completed");

}
catch (Exception ex)
{
Response.Write("Can not open con ! ");

}
}

Reading Xml file and fill dropdown....

XmlNode eleDestNodeLists;
string FilePath = Request.PhysicalApplicationPath + @"Configuration\" + "UserInfo.xml";
XmlDocument docSource = new XmlDocument();
docSource.Load(FilePath);
Int32 assetid = Convert.ToInt32(Session["assetid"].ToString());
string sbookCode = Session["bookCode"].ToString();
eleDestNodeLists = docSource.SelectSingleNode("/UserInfo/Asset[@assetid='" + assetid + "' and @BookCode='" + sbookCode.ToString() + "']");
foreach (XmlNode xn in eleDestNodeLists.ChildNodes)
{
string abbreviation = xn.Attributes.GetNamedItem("abbreviation").Value;
string id = xn.Attributes["id"].Value;
ddlRole.Items.Add(new ListItem(abbreviation, id));
Page.ClientScript.RegisterStartupScript(typeof(Page), "FillUserName", "setTimeout(\"FillUserName()\",1000);", true);
}