In online mode, you connect to a catalog on a running web server. In this mode your permissions are applied, you can select a locale, and you can see the effects of any localization on the catalog. You can see only those objects for which you have the appropriate permissions. BothPresentation Services and the web server must be running for you to open catalogs in online mode. Use online mode when you want to make minor incremental changes or additions to the catalog, such as changes to permissions, updates to a single object, or migration of new objects to a production environment.
Note:
* You can open a catalog in one of two modes - online or offline. Both modes can operate against an actual production catalog, with no need for any downtime. *Repository changes can be done in either online or offline mode. Online mode is when BI Server is actively reading the repository file (when a user is logged in). Offline is when BI Server is idle. Best practice is to develop in Offline mode. Minor changes can be made when in online mode.

Before you can run Oracle Business Intelligence 11g Installer, you must first create required Oracle Business Intelligence schemas in an unhardened database. You use a tool called the Repository Creation Utility (RCU) to create these schemas with the appropriate permissions and data.

Explanation
The Oracle Business Intelligence (BI) Administration Tool can be used to build, modify, enhance, and manage an Oracle BI repository.
C: To add a new user to a repository
1 Open a repository in the Administration Tool.
2 Display the security manager by selecting Manage > Security.
3 Select Action > New > User to open the User dialog box.
4 Type a name and password for the user.
5 If you want to log queries for this user in the query log, change the query logging level to 1 or 2.
6 Click OK.
This creates a new user with default rights granted to it.
Note: What is Oracle BI Admin Tool/Oracle Business Intelligence Administration Tool?
Oracle Business Intelligence Administration Tool is Used to manage OBIEE server Available only for Windows operating systems.
A Windows application that allows the BI Server administrator to create & edit repositories.
Can edit repositories in either online or offline mode.
Having a session manager and a cache manager in online mode.

Steps for Creating Aggregate Tables in OBIEE
1.Create all Dimension Tables, Fact Tables & Hierarchies, which are required to be aggregated.
2.Go to ToolsaUtilities (from Administration tool menu bar), a dialog box will pop up with all available utilities.
3.Select Aggregate Persistence Wizard, and then click Execute Button.
4.Now Select appropriate path where you need to generate Aggregate Table SQL.
Note : Click Generate DDL file for first time generation of Aggregate Table
Click Next, to move to next page (Select Business Model & Measure Page)
In Select Business Model & Measure Page, Select Appropriate Business Model & then select
associated Fact / Measure.

Etc.

Explanation
You can define calculations in either of the following ways:- Before the aggregation, in the logical table source. For example:sum(col_A *( col_B))- After the aggregation, in a logical column derived from two other logicalcolumns. For example:sum(col A) * sum(col B)