Designing and implementing a versatile data access tier for an ASP.NET application

using System;
using System.Web;
using System.Diagnostics;
using System.Configuration;
using System.Text;



namespace HttpTraceModule
{
	/// <summary>
	/// It used to record errors on the presentation layer(PL)
	/// </summary>
	public class HttpTraceModule:IHttpModule
	{
		 
		/// <summary>
		/// Event Log for the Presentation Layer
		/// </summary>
		 EventLog elPL;
		/// <summary>
		/// 
		/// </summary>
		public HttpTraceModule()
		{
			// Initialize  Trace Listener
			string strLog = ConfigurationSettings.AppSettings["plLog"];
			string strSource = ConfigurationSettings.AppSettings["plSource"];
			string strMachine = ConfigurationSettings.AppSettings["plMachine"];
			if(EventLog.SourceExists(strLog,strMachine))
			{
				elPL = new EventLog(strLog,strMachine,strSource);
			}

		}

		/// <summary>
		/// interface contract method
		/// </summary>
		/// <param name="httpApplication"></param>
		public void Init(HttpApplication httpApplication)
		{
			// Subscribe HttpApplication events
           httpApplication.BeginRequest += new EventHandler(Application_BeginRequest);
		   httpApplication.EndRequest += new EventHandler(Application_EndRequest);
		}
		/// <summary>
		/// interface contract method
		/// </summary>
		public void Dispose()
		{
          
  
		}
		/// <summary>
		/// Writes errors on the log of the Presentation Layer 
		/// </summary>
		/// <param name="oException"></param>
		/// <param name="oContext"> </param>
		private void WriteError(HttpContext oContext,Exception oException)
		{
			StringBuilder oBuilder = new StringBuilder();
			// Record the requested URL and the client
			oBuilder.Append("An Error took place, while attempting to request  the  URL: ");
			oBuilder.Append(oContext.Request.RawUrl);
			oBuilder.Append("**");
			oBuilder.Append("Client Address:");
			oBuilder.Append(oContext.Request.UserHostAddress);
            oBuilder.Append("**");
			//  Record the error message
			if( oException != null)
			{
				oBuilder.Append( oException.Message);
			}
			if(elPL != null)
			{
				elPL.WriteEntry(oBuilder.ToString(),EventLogEntryType.Error);
			}

		}


		/// <summary>
		/// Callback method  for the event HttpApplication.EndRequest 
		/// It is used to record all errors on the log of the Presentation Layer 
		/// </summary>
		/// <param name="source"></param>
		/// <param name="e"></param>
		private void Application_EndRequest(object source, EventArgs e)
		{
			HttpApplication hApplication = (HttpApplication) source;
			HttpContext oContext = hApplication.Context;
			Exception oException = oContext.Error;
			if(oException != null)
			{
				this.WriteError(oContext,oException);
			}
		
		}

		/// <summary>
		/// Callback method  for the event HttpApplication.BeginRequest
		/// </summary>
		/// <param name="source"></param>
		/// <param name="e"></param>
		private void Application_BeginRequest(object source, EventArgs e)
		{
			HttpApplication hApplication = (HttpApplication) source;
			HttpContext oContext = hApplication.Context;
			
		}


	}
}