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Microsoft® Windows® DNA Overview
Windows Distributed interNet Application (DNA) is a general architecture that describes how to build three-tiered applications for the Windows platform. A Windows DNA application can be segmented into three logical tiers of functionality: presentation services, business services, and data services. The Windows DNA technical articles provide more information on how to build applications based on the Windows DNA framework.
Presentation Services
The Presentation tier is responsible for gathering information from the user, sending the user information to the business services for processing, receiving the results of the business services processing, and presenting those results to the user. The presentation tier may be based on a browser such as Internet Explorer or on a Win32® client built with Visual Studio® or Microsoft Office.
The Internet Explorer code samples demonstrate how XML can be displayed in a browser. The Visual Studio® code samples demonstrate how XML can be used in Win32® clients.
Business Services
The Business Logic tier is responsible for receiving input from the presentation tier, interacting with the data services to perform the business operations that the application was designed to automate (for example, income tax preparation, order processing, and so on), and sending the processed results to the presentation tier. Middle-tier components that contain business logic are built with the Visual Studio languages.
The Visual Studio code samples show how components built with Visual Studio can read and write XML data. In addition, the BizTalk™ JumpStart Kit demonstrates how to generate Visual Studio middle-tier components based on an XML schema.
Data Services
The Data tier is responsible for the storage of data, retrieval of data, maintenance of data, and integrity of data. Relational and nonrelational data is accessed via ActiveX® Data Objects (ADO).
The ADO code samples show how ADO supports XML and how data can be expressed as XML documents. The BizTalk Framework provides a format for creating XML documents containing data. In addition, the SQL Server™ XML Technology Preview enables the use of familiar SQL statements to retrieve SQL Server data in XML format on the Web.
The Visual Studio Interoperability Center 
provides developer-focused
resources to simplify integration across a wide range of applications,
databases, networks, and management environments. Learn how XML can be
used to provide interoperability in Windows DNA applications.