Get started with asp.net ---- data access

Because we are designing an asp.net + xml + delphi three-tier design
So I am sorting out a simple item.
The following describes how to access xml, access, and mssql data.
Protected DataSet LoadMyPBData ()
{
String sourceXml = Server. MapPath ("phone. xml ");
DataSet dataSet = new DataSet ();
Try
{
DataSet. ReadXml (sourceXml );
}
Catch (Exception e)
{
DataSet = null;
}
Return dataSet;
}
Void Page_Load (object sender, EventArgs e)
{
If (! (Page. IsPostBack ))
{
Gridv. DataSource = LoadMyPBData ();
Gridv. DataBind ();
}
}
-------------------------------
String StrSql = "Data Source = 127.0.0.1; Initial Catalog = dotnet; persist security info = True; user id = sa; password = 1234; packet size = 4096 ";
SqlConnection MyConn = new SqlConnection (StrSql );
MyConn. Open ();
String CommSql = "select * from gbook order by id desc ";
SqlDataAdapter adp = new SqlDataAdapter (CommSql, MyConn );
DataSet ds = new DataSet ();
Adp. Fill (ds );
DataGrid1.DataSource = ds;
DataGrid1.DataBind ();
MyConn. Close ();
---------------------------------------
If (! IsPostBack)
{
OleDbConnection MyConnection = new OleDbConnection ("Provider = Microsoft. Jet. OLEDB.4.0; Data Source =" + Server. MapPath ("new. mdb "));
OleDbDataAdapter myCommand = new OleDbDataAdapter ("SELECT id, typename FROM bb", MyConnection );
DataSet ds = new DataSet ();
MyCommand. Fill (ds, "bb ");
DropDownList2.DataSource = ds. Tables ["bb"]. DefaultView;
DropDownList2.DataTextField = "typename ";
DropDownList2.DataValueField = "id ";
DropDownList2.DataBind ();