Writing a Custom WebService for SharePoint

using System;
using System.Data;
using System.Web;
using System.Web.Services;
using System.Web.Services.Protocols;
using Microsoft.SharePoint;

[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
public class Service : System.Web.Services.WebService
{
    //DataView dv;
    public Service()
    {

        //Uncomment the following line if using designed components 
        //InitializeComponent(); 
    }

    [WebMethod]
    public string HelloWorld()
    {
        return "Hello World";
    }
    [WebMethod]
    public DataSet getTasks()
    {
        try
        {
            DataSet dv = new DataSet();
            DataTable dt = new DataTable();
            //dv = new DataView();
            SPSite obsite = new SPSite("http://vlnrm:100/Prasad");
            SPWeb currentWeb = obsite.AllWebs["Prasad"];
            dt.TableName = "Prasad";
            dt.Columns.Add("Title");
            dt.Columns.Add("Status");
            dt.Columns.Add("Priority");
            dt.Columns.Add("StartDate");
            SPList Tasks = currentWeb.Lists["Tasks"];
            string strTitle = string.Empty;
            if (Tasks != null)
            {
                SPListItemCollection listItems = currentWeb.Lists["Tasks"].Items;
                if (listItems.Count > 0)
                {
                    foreach (SPListItem item in listItems)
                    {
                        if (item["Title"] != null)
                        {
                            strTitle = item["Title"].ToString();
                        }
                        else
                        {
                            strTitle = "--";
                        }
                        DataRow drow = dt.NewRow();
                        drow["Title"] = strTitle;
                        drow["Status"] = item["Status"].ToString();
                        drow["Priority"] = item["Priority"].ToString();
                        drow["StartDate"] = item["StartDate"].ToString();
                        dt.Rows.Add(drow);

                    }
                    dv.Tables.Add(dt);
                }
            }
            return dv;
        }
        catch (Exception ex)
        {
            string str = ex.ToString();
            Console.WriteLine(str);
            DataSet dsErr = new DataSet(); ;
            DataTable dt1 = new DataTable();
            dt1.Columns.Add("err");
            DataRow dr1;
            dr1 = dt1.NewRow();
            dr1["err"] = ex.ToString();
            dt1.Rows.Add(dr1);
            dsErr.Tables.Add(dt1);
            return dsErr;
        }
    }

}