In n-tier application development, the business-services tier provides most of an application's functionality. This tier handles the bulk of application-specific processing and enforces an application's business rules. Business logic built into custom components bridges the client environments and the data-services tier.
The business-services tier is implemented as both a set of server applications and a run-time environment for COM components. This tier includes Microsoft® BackOffice® Server products such as Microsoft Transaction Server version 2.0, Microsoft Internet Information Server version 4.0, and Microsoft Message Queue Server version 1.0. In addition, this tier hosts the Active Server Pages (ASP) pages that the client calls. ASP pages contain a robust mixture of HTML, DHTML, and scripting languages; calls to custom business objects are made from the ASP environment. The business objects in turn call the data access components such as ActiveX® Data Objects that cross the boundary into the data-services tier and return requests to the client. As you use the BackOffice Developer's Guide, you will learn how to program to this n-tier development model and write variations that suit your particular needs.
The Windows DNA programming model locates the following application services at the business-services tier: