Visual Basic 6 Business Objects
In Chapter 2, we looked at the logical parts, or tiers, of a client/server application. In this chapter, we'll walk through the common physical architectures that we're likely to encounter as we develop our applications. We'll look at how the different logical tiers of the application fit into each physical model, and we'll discuss some different options in each case.
The physical architectures that we'll discuss include:
- 2-tier (client workstations and a database server)
- 3-tier (client workstations, application servers, and database servers)
- n-tier (traditional or browser-based client, Web server and/or application servers, and database servers)
We'll also look at some specific design concerns for our business objects. Our UI-centric business objects need to communicate with a user-interface, and there are some issues that we need to be aware of when we're designing our objects to make this work well.
Well discuss how the Component Object Model (COM) can be used by our objects to communicate with each other. There are some serious performance concerns we need to consider as we implement our objects and their communications. Fortunately there are a number of mechanisms we can use to minimize the performance impact and well examine a number of them.
Additionally, our objects need to be persistent. This means that they must have a way to be saved and restored from a database. The CSLA (Component-based Scalable Architecture) provides for this, and in this chapter we'll get right into the details on how it's all done. As ever, what sounds easy enough in principle can be challenging in practice, so we'll take a good look at some of the techniques available in Visual Basic to make it fast and easy to persist objects.