A Task Management System using Three Layer Architecture

using System;
using System.Data;
using System.Configuration;
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;

/// <summary>
/// Summary description for AdminGateWay
/// </summary>
public class AdminGateWay
{
    DataExecuteClass DEC = null;
	public AdminGateWay()
	{
		//
		// TODO: Add constructor logic here
		//
	}
    public DataTable SelectAllEmployeeData()
    {
        string selectString = "SELECT EmployeeId, EmployeeName, EmployeeAddress, EmployeeContactNo, EmployeeDesignation, EmployeeEmail, EmployeeJoinDate  FROM t_Employee where EmployeeRole='Employee'";
        DEC = new DataExecuteClass();
        DataTable dt = DEC.getDataSet(selectString).Tables[0];
        return dt;
    }
    public DataTable SelectAllUserData()
    {
        string selectString = "SELECT EmployeeId, EmployeeName, EmployeeAddress, EmployeeContactNo, EmployeeDesignation, EmployeeEmail, EmployeePassword, EmployeeJoinDate  FROM t_Employee where EmployeeRole='User'";
        DEC = new DataExecuteClass();
        DataTable dt = DEC.getDataSet(selectString).Tables[0];
        return dt;
    }
    public DataTable SelectAllAdminData()
    {
        string selectString = "SELECT EmployeeId, EmployeeName, EmployeeAddress, EmployeeContactNo, EmployeeDesignation, EmployeeEmail, EmployeePassword, EmployeeJoinDate  FROM t_Employee where EmployeeRole='Admin'";
        DEC = new DataExecuteClass();
        DataTable dt = DEC.getDataSet(selectString).Tables[0];
        return dt;
    }
    public DataTable SelectAllProject()
    {
        string selectString = "SELECT * from t_Project";
        DEC = new DataExecuteClass();
        DataTable dt = DEC.getDataSet(selectString).Tables[0];
        return dt;
    }
}