11i Top level directories

1.APPL_TOP
2.AU,FND,AD
3.ORA_TOP
4.DB_TOP
5.DATA_TOP

Core Technology Directories

In APPL_TOP admin,ad,au,fnd are called Core Technology Directories

Admin:

this contain files and scripts by AD utilities during upgrade and maintenance.

A SID directory contains log and out and restart containing upgrade log,output and restart files respectively
this directory contain scripts according 11i but in R12 it is changed to inst_top directory.
its contains adovers.env file,text files containing product related information used by auto upgrade and application contextfile(in R12 INST_TOP)


AU:


This contains files of all the products. Consolidated in a single location for optimal processing

A form directory contain forms of all products in .fmb format.
A report directory containing all reports of all products
A plsql directory contains library files which are used by reports
A resource directory containing libraries used by forms.


FND:

 It contains scripts and programs that are used as the foundation for all application products to build data dictionaries, forms and c object libraries.

 A secure directory contains .dbc file used in authentication process

the fnd directory contains fndenv.env environment file it is called by main environment file.(FND_TOP)

COMMON_TOP:

It is top level directory containing files used by different oracle application products and third party products.
COMMON_TOP/admin: it is default directory for log and out directory
             log:containing log files written by concurrent manager
             Out:containing out files written by concurrent manager
             install:containing scripts and log file used by rapid install
             scripts: to start services like concurrent manager and listener.
             Html: contain application html based sign-on screen and oracle html based applications HTML files.

ORA_TOP:

 It is called application technology stack.it contain two top level directories 806 home and IAS home

    806Home: oracle home for Developer6i products like forms,reports and discoverer in the respective sub directories forms60,reports60 and discwb4
             the product libraries of 806 home is used for relinking oracle executable

     IAS home:It contain oracle home 9i application server which is powered by Apache server. it contain java libraries/code for running Apache server
              Apache related files located under fallowing sub directories

              ias_home/Apache:contain all Apache related files and directories
              ias_home/Apache/Apache: contains all Apache configuration and executable files
              ias_home/Apache/Apache/jdk/: it contain java developer kit in jdk sub directory
              ias_home/Apache/Apache/jsdk: java software development kit in Jdk sub directory
              ias_home/Apache/Apache/jserv:servlet related files
              ias_home/Apache/Apache/jsp: ojsp configuration files
              ias_home/Apache/Apache/modplsql:modplsql executales and related files

Oracle Application Database file system:
It contain two top level directories DB_TOP and DATA_TOP

1. DB_TOP
 
    It contain all files needed for running and maintaining application database. It is the Oracle hoe for Application Database.
     Admin: It contain all the dump files used by the database(bdump,cdump,udump)
     Dbs: it contain init.ora file
      Network/Admin- contain Tnsnames.ora and listener.ora files

2. Data_TOP:
 
 It conatains all the data files of applications. The dbf files related to data,index redologs and system etc