Application Architecture Single Tier Architecture ,Two Tier Architecture, Three Tier Architecture,Four Tier Architecture

Application Architectures
Single Tier Architecture :
Data and Application will be running in the same memory. Application and Data both are on the same system.
                                    Eg:       C / Java / .Net Applications working files

Two Tier Architecture :
Data is in one memory and Application is in another memory. Application and Data both can be on the same system or different systems in a network.
                        Eg:
                                    D2k Form / Reports/ Java Console Application / VB Forms ( Any Desktop Application )





Three Tier Architecture :
It is a Web Application. Web Application can be Java / .Net  / Oracle Applications or any other application working with Application Servers.









Four Tier / Multi-Tier Architecture :

It is an Enterprise Application.









Middleware :
Java EJB Components are used as Middleware Components.
Some Middleware Components can be Distributed.

If Application –Tier  and Middle-Tier are on the Same system, then it is called as Enterprise Application.

If multiple Middleware components are running on different systems in a network, then it is called as distributed application.


Oracle Applications architecture
Oracle Applications architecture is a framework for multi-tiered, distributed computing, that supports Oracle Applications products.  In this model, various services are distributed among multiple levels, or tiers.

  

A Service is a process or group of processes running on a single machine that provides a particular functionality. The HTTP service, for example, is a process that listens for and processes HTTP requests, and the Forms service is a process that listens for and processes requests for Oracle Forms.

TIER
A tier is a grouping of services, potentially across physical machines.
desktop tier, which provides the user interface display. Only the presentation layer of Oracle Applications is on the desktop tier in the form of a plug-in to a standard Internet browser.

The application tier, which manages Oracle Applications and other tools;
The tiers that, manages the Oracle database is a Database-Tier;
Clients are generally windows
Application and Data base on Linux/Sun Solaris
The Desktop Tier
The client interface is provided through HTML for the Self-Service interface, and a Java applet for the professional, forms-based interface using a Java-enabled Web browser. The desktop client with Oracle JInitiator downloads the applet on demand and the applet is cached locally for future use.


Forms Client Applet

The forms client applet is a general-purpose presentation applet that supports all Oracle Applications forms-based products, including those with customizations and extensions. The Forms client applet is packaged as Java archive (JAR) files. The JAR files contain all Java classes required to run the presentation layer of Oracle Applications forms. The Forms client applet and commonly used JAR files are downloaded from the Web server at the beginning of the client’s first session. Other less commonly used JAR files are downloaded as needed. The JAR files remain in the disk cache on the desktop, ready for future sessions, minimizing network traffic. All updates are installed on the application tier and downloaded to the client automatically through the use of the JInitiator-enabled Web browser.


Oracle JInitiator

The forms client applet must run within a Java Virtual Machine (JVM) on the desktop. For Oracle Applications, the JVM is supplied by Oracle JInitiator. Oracle JInitiator works in conjunction with the Web browser. It is implemented on the desktop client as a plug-in (Netscape Communicator/ Mozilla Browser) or ActiveX component (Microsoft Internet Explorer). When a user enters the desired Oracle Applications signon URL within theWeb browser, Oracle JInitiator is executed. If Oracle JInitiator has not been installed, the Web browser prompts the user to download the necessary installation executable to the desktop client. Once installed, Oracle JInitiator runs the Forms client applet and starts an Oracle Applications session.

The Application Tier

The application tier hosts the servers that process the business logic and provides the communication between the desktop tier and the database tier. This tier is also referred to as the middle tier. Oracle 9i Application Server (9iAS) provides the technology stack used on the application tier. Six servers comprise the application tier for Oracle Applications:

■ Web server
■ Forms server
■ Concurrent Processing server
■ Reports server
■ Discoverer server
■ Admin server




Load Balancing

The application tier supports load balancing among many of its servers to provide higher availability, fault tolerance, reliability, and optimal scalability. Load balancing occurs when there are multiple installations of the following:

■ Web server
■ Forms server
■ Reports server
■ Concurrent Processing server
■ Discoverer server

The Database Tier


The database tier contains the database server, which stores all the data maintained by Oracle Applications. It also contains some processing code that is stored in the database to optimize performance. In Release 11i, the database includes the Oracle Applications online help information as well. More specifically, the database tier contains the Oracle data server files and Oracle Applications database executables that physically store the tables, indexes, and other database objects for your system. In general, the database server does not communicate directly with the desktop clients, but rather with the servers on the application tier, which mediate the communications between the database server and the client.

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