Oracle 9i Application Architecture

Client/Server Architecture

The client runs the database application that accesses database information and interacts with a user. The server runs the Oracle software and handles the functions required for concurrent, shared data access to an Oracle database.

Distributed processing is the use of more than one processor to perform the processing for an individual task.

Multitier Architecture

In a multitier architecture environment, an application server provides data for clients and serves as an interface between clients and database servers. This architecture is particularly important because of the prevalence of Internet use.


A client initiates a request for an operation to be performed on the database server. The client can be a Web browser or other end-user process. In a multitier architecture, the client connects to the database server through one or more application servers.

Application Servers

An application server provides access to the data for the client. It serves as an interface between the client and one or more database servers, which provides an additional level of security.

Database Servers

A database server provides the data requested by an application server on behalf of a client. The database server does all of the remaining query processing.

Oracle Net Services

Oracle Net Services provides enterprise-wide connectivity solutions in distributed, heterogeneous computing environments. Oracle Net Services enables a network session from a client application to an Oracle database.


After a network session is established, Oracle Net Services acts as a data courier for the client application and the database server. It is responsible for establishing and maintaining the connection between the client application and database server, as well as exchanging messages between them.


Oracle Net Services provides location transparency, centralized configuration and management, and quick out-of-the-box installation and configuration.

Internet Scalability

Oracle Net Services enables you to maximize system resources and improve performance. Oracle's shared server architecture increases the scalability of applications and the number of clients simultaneously connected to the database.The Virtual Interface (VI) protocol places most of the messaging burden on high-speed network hardware, freeing the CPU for more important tasks.

Internet Security

Network security is enhanced with features like database access control and Oracle Advanced Security.

How Oracle Net Services Works

The Oracle protocols take SQL statements from the interface of the Oracle applications and package them for transmission to Oracle through one of the supported industry-standard higher level protocols or programmatic interfaces. The protocols also take replies from Oracle and package them for transmission to the applications through the same higher level communications mechanism.

The Listener

When an instance starts, a listener process establishes a communication pathway to Oracle. When a user process makes a connection request, the listener determines whether it should use a shared server dispatcher process or a dedicated server process and establishes an appropriate connection.

Service Information Registration

Dynamic service registration reduces the administrative overhead for multiple databases or instances. Information about the services to which the listener forwards client requests is registered with the listener. Service information can by dynamically registered with the listener through a feature called service registration or statically configured in the listener.ora file.

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