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

using System;
using System.Diagnostics;
using System.Configuration;

namespace BLT
{
	/// <summary>
	/// Summary description for BLBasis.
	/// </summary>
	public class BLBasis
	{

		// EventLog for Buisness Logic Tier
		protected static EventLog daEventLog;
		// strings to connect EventLog
		protected static string strLog;
		protected static string strSource;
		protected static string strMachine;

		protected static decimal dConsumeTaxRate;
		public BLBasis()
		{
			
		}

		static BLBasis()
		{
			// strings to connect the EventLog
			strLog = ConfigurationSettings.AppSettings["blLog"];
			strSource = ConfigurationSettings.AppSettings["blSource"];
			strMachine = ConfigurationSettings.AppSettings["blMachine"];
			dConsumeTaxRate = Convert.ToDecimal(ConfigurationSettings.AppSettings["consumeTaxRate"]);
			// Create an instance from EventLog
			if(EventLog.SourceExists(strLog,strMachine))
			{
				daEventLog = new EventLog(strLog,strMachine,strSource);
			}
		}

		/// <summary>
		/// Writes error messages in to the EventLog
		/// </summary>
		/// <param name="strMessage"></param>
	    protected virtual void ErrorLog(string strMessage)
		{
			// write in Windows EventLog
			if(daEventLog!=null)
			{
				daEventLog.WriteEntry(strMessage,EventLogEntryType.Error);
			}
			// throw an error to the buisness access tier
			Exception oException= new Exception("An error occured in  BLTier ");
			throw oException;
		}

		/// <summary>
		///  Writes error messages in to the EventLog
		/// </summary>
		/// <param name="strMessage"></param>
		/// <param name="oException"></param>
		protected virtual void ErrorLog(string strMessage,Exception oException)
		{
			// write in Windows EventLog
			if(daEventLog!=null)
			{
				string oMessage = oException.Message + " " + strMessage;
				daEventLog.WriteEntry(oMessage,EventLogEntryType.Error);
			}
			// throw an error to the 
			Exception oExcept= new Exception("An error occured in  BLTier");
			throw oExcept;
		}
       

		/// <summary>
		/// Writes warning messages on the EventLog
		/// </summary>
		/// <param name="strMessage"></param>
		protected void WarningLog(string strMessage)
		{
			// write in Windows EventLog
			if(daEventLog!=null)
			{
				daEventLog.WriteEntry(strMessage,EventLogEntryType.Warning);
			}
		}
	}
}