1.
System.IO.Path
string fullPath = Path.GetFullPath("db1.mdb");
2.
HttpContext.Current.Server.MapPath
3.
Environment.CurrentDirectory
HttpRuntime.AppDomainAppPath
AppDomain.CurrentDomain.BaseDirectory
Application.StartupPath.ToString();
AppDomain.CurrentDomain.BaseDirectory;
HttpRuntime.AppDomainAppPath