Understanding Client/Server Databases
Another client/server environment found on corporate networks is the shared database . Shared databases allow users to access information that is held centrally on a database server. This central database may hold customer information, employee information, or data related to a particular project.
The centralized database is certainly not a new concept to computing; large database systems were an integral part of early mainframe and miniframe environments. Oracle Corporation's powerful Oracle client/server database environment started out as a product for the miniframe environment but has evolved into a multiplatform client/server system that can also be run on Pentium-based LAN servers.
Client/server databases require both a dedicated server and a client front end. The database server software, also referred to as the database engine , is designed to accept requests for information (a request to a database for information is called a query ) from clients on the network. The actual query is made by the client software on the user's computer. Because the exchange of data between the database server and the database client is transparent to the user, the features and functionality provided by the database client will be the same as if the database resided locally on the user 's computer.
An excellent example of a client/server database system is Microsoft's SQL Server (SQL stands for Structured Query Language ; it is the language used by the database client software to send queries to the database server). SQL Server is an add-on product that runs on an existing Windows server.
The client front end used to query SQL Server is Microsoft Access. Microsoft Access is a powerful standalone database software application in its own right. It provides all the tools needed to create complex relational databases. Figure 11.15 shows an Access window and an open Access/SQL project.
Figure 11.15. Shared databases need a client front end, such as Microsoft Access.
Client/server technology has been changing by leaps and bounds because of the Internet and the desire of companies to try their hands at e-commerce. Any time you book an airline reservation online or order a book from an online bookstore, you are taking advantage of client/server database technology. We will talk more about e-commerce in the section "The Internet and Your Corporate Presence" in Chapter 16, "Hosting a Web Site".