The simplest type of distributed computing is two-tier client/server. In this type of application, the data processing is moved off the user's machine on to a dedicated database server machine. Two-tier client/server is the most common type of client/server application built today. It offers significant benefits over a simple application, since the processing of data is centralized and becomes a shared resource between all the users:
Still, with two-tier client/server, the only work that has really been moved off the user's machine is the data management - storing and retrieving data. The user-interface and any processing done by the application remain pretty much where they were:
The primary difference lies in the role of the data service objects. In this model, they have to do much less work, since a lot of the data processing is moved to the database server - usually in the form of stored procedures and triggers written in SQL. Again, we'll talk in more detail about these data service objects in Chapter 2.