Chapter 2 DATABASE DESIGN FOR SQL SERVER 2000
Chapter 2 DATABASE DESIGN FOR SQL SERVER 2000 93 In this way only data that is needed is sent back to the client, and thereby multiuser access is provided, in contrast to non-client/server desktop database systems that prefer singular access and have difficulty handling multiuser functionality. This process is shown in Figure 2.12. In a non-client/server desktop architecture, the whole database resides on the client s machine; the client then processes the query locally on the database and finds records as required. This process results in wasted disk space and is difficult to set up in a multiple- user environment. The server is concerned with uses such as concurrency, security, and backing up data. The client-side application is implemented with a nice user interface and might contain queries and forms. The roles of each computer are not, however, carved in stone, and depending on the interactions required in any given system, many machines may take part. The process of dividing up processing across many machines creates a multi-layered environment. Each layer in the environment is referred to as a tier and each tier has a specific role to play in the overall system. Application development and choice of model is a crossover stage between the logical development and the physical database structure. At times the choice of the number of tiers is accomplished before the physical database implementation. Others choose to prepare the database first. Neither is absolutely correct, but it is a good idea to have some idea of the model before determining the final physical data structure. One- and Two-Tier Systems A one-tier system in a PC environment dates back 25 or more years to an environment where the only way to share data was to use the sneaker net approach. In other words, copies of the data were made and distributed manually. This approach was adequate at best and caused many headaches for anyone trying to implement a multiple-user environment. Particularly difficult was the merging of updates from multiple copies of the data. With a single-tier approach, one computer performs all the processing required to view, update, and store the data. Many products use this technique for small, single-user database systems, but this tech
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