In this article, we will drill down deeper in to the design of a n-tier architecture and our focus will be on the data access tier(DAT). Our goal is to design and implement an appropriate data access tier(DAT) for scalable, reliable and interoperable web application. I have divided this article in to two major parts. In the first part, we will discuss about architectural goals, typed DataSet, EventLogs and HttpModules, which are helpful to understand the second part of this article. We will build in the second part a small(but fine) n-tier application and our focus will be on design and implementation of data access tier. You need a SqlServer (database: Northwind) and VS.net to follow this article.