请教编程上的问题

using System;
using System.Collections;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
namespace mySqlData
{
    /// <summary>
    /// ClassConn 的摘要说明。
    /// </summary>
    public class Myconnection        //数据库连接类
    {
        public Myconnection()
        {
            //
            // TODO: 在此处添加构造函数逻辑
            //
        }
        public SqlConnection connstr;    //连接字符串
        public string getconnstr()     //获取连接字符串
        {
            string constr;
            constr = System.Configuration.ConfigurationSettings.AppSettings["connectionString"];
            return constr;
        }
        public void open()       //打开数据库
        {
            string constr;
            constr = getconnstr();
            connstr = new SqlConnection(constr);
            connstr.Open();
        }
        public void close()       //关闭数据库
        {
            connstr.Dispose();
            connstr.Close();
        }
        public void execsql(string sql)    //执行sql语句
        {
            open();
            SqlCommand cmd = new SqlCommand(sql, connstr);
            cmd.ExecuteNonQuery();
            close();
        }
        public DataSet dataset(string sql)   //返回DataSet对象
        {
            open();
            SqlDataAdapter rs = new SqlDataAdapter(sql, connstr);
            DataSet ds = new DataSet();
            rs.Fill(ds);
            return ds;
        }
        public DataView dataview(string sql) //返回DataView对象
        {
            DataSet ds = new DataSet();
            ds = dataset(sql);
            DataView dv = new DataView(ds.Tables[0]);
            return dv;
        }
        public SqlDataReader datareader(string sql) //返回DataReader对象
        {
            open();
            SqlCommand cmd = new SqlCommand(sql, connstr);
            SqlDataReader dr = cmd.ExecuteReader();
            return dr;
        }
    }
}