Implementing data access functionality

Implementing data access functionality is a core activity of most developers working with the .NET Framework, and the data access layers they build are an essential part of their applications. This article outlines five ideas to consider when building a data access layer with Visual Studio .NET and the .NET Framework. The tips include taking advantage of object-oriented techniques and the .NET Framework infrastructure by using base classes, making classes easily inheritable by following guidelines, and carefully examining your needs before deciding on a presentation method and external interface.
 Contents
Rule 1: Use Object-oriented Features
Rule 2: Adhere to the Design Guidelines
Rule 3: Take Advantage of the Infrastructure
Rule 4: Choose Your External Interface Carefully
Rule 5: Abstract .NET Framework Data Providers
Conclusion

If you're developing a data-centric application targeting the Microsoft® .NET Framework, you'll eventually need to create a data access layer (DAL). You probably know that there are benefits of building your code in the .NET Framework. Because it supports both implementation and interface inheritance, your code can be more reusable, especially by developers across your organization using different Framework-compliant languages. In this article, I'll present five rules for developing a DAL for your .NET Framework-based applications.

Refer these links

http://msdn.microsoft.com/en-us/magazine/cc188750.aspx
http://www.simple-talk.com/dotnet/.net-framework/.net-application-architecture-the-data-access-layer/