Single-Tier, Two-Tier, and Multitier Database Architecture

Date: 2015-10-07; view: 489.

Local databases are often called single-tier databases. A single-tier database is a database in which any changes--such as editing the data, inserting records, or deleting records--happen immediately. The program has a more direct connection to the database.

In a two-tier database, the client application talks to the database server through database drivers. The database server takes the responsibility for managing connections, and the client application is largely responsible for ensuring that the correct information is being written to the database. A fair amount of burden is put on the client application to make sure the database's integrity is maintained.

In a multitier client/server architecture, the client application talks to one or more application servers that, in turn, talk to the database server. These middle-level programs are called application servers because they service the needs of the client applications. One application server might act as a data broker, responding to and handling data requests from the client and passing them on to the database. Another application server might only handle security issues.

Client applications run on local machines; the application server is typically on a server, and the database itself might be on another server. The idea behind the multitier architecture is that client applications can be very small because the application servers do most of the work. This enables you to write what are called thin-client applications.

Another reason to use a multitier architecture is management of programming resources. The client applications can be written by less experienced programmers because the client applications interact with the application server that controls access to the database itself. The application server can be written by more experienced programmers who know the rules by which the database must operate. Put another way, the application server is written by programmers whose job is to protect the data from possible corruption by errant client applications.

Although there are always exceptions, most local databases make use of the single-tier architecture. Client/server databases use either a two-tier or a multitier architecture.

So how does this affect you? Most applications you write with Delphi for use with a client/server database will be client applications. Although you might be one of the few programmers given the task of writing server-side or middle-tier applications, it's a good bet that you will write primarily client applications. As an application developer, you can't talk directly to these database servers. Let's look next at how a Delphi application talks to a database.