Chapter 16 Building Middle-Tier Components

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Chapter 16
Building Middle-Tier Components

IN THIS CHAPTER WE'LL discuss the concepts of distributed architecture and the role of components and multiple tiers in developing data-driven applications. We'll focus on the drift from client/server architectures to multi-tier architectures and we'll present a few simple examples to demonstrate the principles of middle-tier components and how to deploy them on a remote server.

We'll also discuss how to use existing COM components (including ActiveX controls) and COM+ applications with .NET clients. Every corporation has made an investment in COM components, which you aren't going to throw away. Whether these components you've developed as recently as a year ago can be called ''legacy" components is a different story.

Finally, we'll show you how to deploy .NET components on remote servers and allow clients to request their services over the network, or the Web. We'll touch the subjects of Web services and remoting, which are central in deploying business components in a distributed environment.

From Client/Server to Multiple Tiers

The dominant architectural model for data-driven applications today is the client/server model. Most applications written today in small business environments are based on the client/server model and most VB6 developers are quite familiar with it. The client/server model distributes the processing on two layers: the database, which is a powerful machine running the database management system, and the clients (Figure 16.1). The program running on the client is responsible for interacting with the user: it accepts user input, validates it, and makes requests to the server. When the server sends the data, the client application presents it to the user, using a rich Windows interface.

The advantage of this architecture is that the workload is distributed on two different layers. The database server is optimized for performing queries against a database. The basic requirements of the database server are very fast disk systems (usually RAID systems) and large (to enormous) amounts of memory. The clients need not be nearly as powerful: a regular workstation will do. The application running on the client is either a Windows application (in which case the client is called rich client, to indicate that the client application can exploit all the resources of the client

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