How to Become Oracle Apps DBA

Oracle Apps Architecture is the first step towards learning anything in oracle apps. This blog entry tries to address this topic.
When Oracle first came out with ERP package it was all character based and basically was a centralized computing architecture. In apps release 10.7, the character release of Applications primarily had the database and it’s end-user forms defined in character based forms. The database was Oracle 7.3.2, and forms version was “SQL forms 3″ (character forms). The users had to telnet to the server to be able to access the applications. After connecting to the server they had to issue the command ‘found’ to be able to invoke the form that used to connect them to the server. The client machines used to connect to the server were primarily dumb terminals. e.g. VT100 etc.
In Release 10.7 there were three options:
1. The original char based
2. Smart Client (which was basically client-server architecture)
3. NCA (Network Computing Architecture)
In a Smart Client Install of 10.7, the database was Oracle 7.3.2 and the front end constituted of Developer 1.3.1 or 1.3.2. The clients used to connect to the server with the help of the named service or TCP/IP link made in the file tnsnames.ora. The SQL*Net protocol or the Net80 protocol was used for connectivity.
In NCA oracle apps was finally available in “The Three Tier Architecture”. There were three distinct “Tiers” now and client side could be much lighter (generally a java enabled browser). This architecture has been taken into release 11 and 11i, and from what I hear and read about release 12, there will not be any major change in this architecture.
The three disctinct “Tiers” in Oracle apps 11i (11.5.10.2 is the latest as of now) are:
1. Desktop Tier
2. Application Tier
3. Database Tier
The following image taken from Oracle Applications Concepts illustrates the three tiers
Lets talk breifly about these tiers individaully:
1. Deskptop Tier: Its is nothing but a simple web browser (Internet explorer or Netscape etc) from which end-user logs into the application. Important thing to remember is that browser has to be java enabled. The componants required on the desktop tier are Forms Client Applet and Oracle Jinitiator.
a. Forms Client Applet:

Most of the Oracle Applications is based on Oracle Forms and Reports (Oracle Developer) and to display oracle forms on a client’s browser an applet is used. This forms client applet displays Oracle Applications screens and support field level validation, multiple windows and list of values (LOVs). The forms client applet is paclaged as Java Archive (JAR) files that contain all java classes for forms applet. These jar files are downoaded from Web server at the beginning of the client’s session and remains in the cache known as Jcache.

b. Oracle Jinitiator:

The Forms Client Applet must run within a Java Virtual Machine (JVM) on the client machine. For Oracle Apps the JVM is provided by Oracle Jinitiator which acts as a plug-in (Active X componant in IE) in the web browser. Please note that for Oracle apps we do not use other JVMs e.g. Microsoft JVM, Sun JVM etc..
When end-user enters the desired Oracle Applications signon URL withing the web browser, the browser will execute the Oracle Jinitiator. If Jinitiator has not been previously installed, end user will be prompted to download the necessary installation executable to the desktop. Once Jinitiator is installed, the forms client applet is started and Oracle Forms sessions is opened.

2. Application Tier : The application Tier, as the name suggest is nothing, but location of application servers. This Tier is sometimes referred to as middle tier and provided business logic and code processing. There are five servers in Applications tier:

a. HTTP server (powered by Oracle Apache)
b. Forms server (This host all you Oracle forms)
c. Concurrent Processing Server
d. Reports Server (host all the Oracle reports)
e. Admin Server

3. Database Tier : The database tier contains the Data Server and holds all the data stored and maintained by Oracle Applications system. There are basically two types of database objests: Data Objects like Oracle apps Tables, Indexes, sequences etc.. and Code Objects like Stored Procedures, Packages, functions,triggers etc..
Important thing to remember is that database tier does not directly communicates with desktop tier, but rather with servers on the middle tier which in turn provides the end-users with the information as required in interface which is more user friendly. Hence almost all the processing is handled at Applications and Database Tier (which are much bigger machines) leaving client machines free of any processing.
At this point you must be having a basic understanding of Oracle Applications Architecture. I suggest that for deeper understaning of the various componants of Oracle Applications, one should carefully read chapter 1 (Applications Architecture) of Oracle Applications Concept Manual (Oracle Applications Concept)