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 CommentGateWay
/// </summary>
public class CommentGateWay
{
    DataExecuteClass DEC = null;
	public CommentGateWay()
	{
		//
		// TODO: Add constructor logic here
		//
	}
    public bool InsertNewComment(Comment commentObj)
    {
        try
        {
            string insertSting = "INSERT INTO t_Comment (CommentBody, TaskId, ProjectId, CommentDate, CommentBy, Attachment) VALUES ('" + commentObj.CommentBody + "', '" + commentObj.CommentTaskId + "','" + commentObj.CommentProjectId + "','" + commentObj.CommentDate + "', '" + commentObj.CommentSenderId+"', '"+commentObj.CommentAttachmentAddress+"'  )";
            DEC = new DataExecuteClass();
            DEC.ExecuteNonQuery(insertSting);
            return true;
        }
        catch
        {
            return false;
        }
    }
    public DataTable SelectAllCommentForSpecificTask(string taskId)
    {
        DEC = new DataExecuteClass();
        string selectString = "select CommentBody, TaskId, ProjectId, CommentDate, CommentBy, Attachment from t_Comment where TaskId = '"+taskId+"'";
        DataTable dt = DEC.getDataSet(selectString).Tables[0];
        return dt;
    }
}