Overview of Application Architecture

There are two common ways to architect a database: client/server or multitier. As internet computing becomes more prevalent in computing environments, many database management systems are moving to a multitier environment.

Client/Server Architecture

Multiprocessing uses more than one processor for a set of related jobs. Distributed processing reduces the load on a single processor by allowing different processors to concentrate on a subset of related tasks, thus improving the performance and capabilities of the system as a whole.
An Oracle database system can easily take advantage of distributed processing by using its client/server architecture. In this architecture, the database system is divided into two parts: a front-end or a client, and a back-end or a server.

The Client

The client is a database application that initiates a request for an operation to be performed on the database server. It requests, processes, and presents data managed by the server. The client workstation can be optimized for its job. For example, it might not need large disk capacity, or it might benefit from graphic capabilities.
Often, the client runs on a different computer than the database server, generally on a PC. Many clients can simultaneously run against one server.

The Server

The server runs Oracle software and handles the functions required for concurrent, shared data access. The server receives and processes the SQL and PL/SQL statements that originate from client applications. The computer that manages the server can be optimized for its duties. For example, it can have large disk capacity and fast processors.

Multitier Architecture: Application Servers

A multitier architecture has the following components:

• A client or initiator process that starts an operation
  
• One or more application servers that perform parts of the operation. An application server provides access to the data for the client and performs some of the query processing, thus removing some of the load from the database server. It can serve as an interface between clients and multiple database servers, including providing an additional level of security.
  
• An end or database server that stores most of the data used in the operation
  

This architecture enables use of an application server to do the following:

• Validate the credentials of a client, such as a Web browser
• Connect to an Oracle database server
• Perform the requested operation on behalf of the client

If proxy authentication is being used, then the identity of the client is maintained throughout all tiers of the connection.