When you need to model many-to-many relationships between dimension tables and fact tables, you can create a bridge table that resides between the fact and the dimension tables. A bridge table stores multiple records corresponding to that dimension. In the Administration Tool, General tab in the Logical Table dialog box contains a check box that you can select to specify that a table is a bridge table.
A bridge table allows you to resolve many-to-many data relationships.
Reference; OBI Server Administration Server Guide, Version 10.1, Identifying Bridge Tables

Note: A level-based measure is a column whose values are always calculated to a specific level of aggregation.
The calculation of this measure is independent of the query grain and used always the aggregation grain of the logical column.
Level-based measures allow :
* to return data at multiple levels of aggregation (the query grain and the level-based column grain) with one single query
* to create share measures (percentage), that are calculated by taking some measure and dividing it by a level- based measure. For example, you can divide salesperson revenue by regional revenue to calculate the share of the regional revenue each salesperson generates.

B: The problem with caching of any kind is how to deal with stale data. How you decide to deal with this depends on how time critical your business intelligence queries happen to be. OBIEE provides a wide variety of mechanisms for dealing with stale data. The cache can be purged automatically at intervals. Caching can be enabled selectively for individual physical tables, so that data in a frequently updated table is never cached.
OBIEE provides a set of ODBC procedures that can be called when ETL processes complete to programmatically purge designated tables. But, by far the best way to selectively purge the cache is to use an event polling table. This table is populated by the client database whenever changes are made to any table (by an ETL process for a data warehouse or by a table-based trigger for an OLTP database). At specified intervals the BI Server polls this event polling table and deletes from its cache any query results that are dependent on the changed data.

Security Manager - is used to setup users, groups, synchronize LDAP users and Groups, set access rights for Objects (tables, columns) and to control over when and what data a user can access.


Note: When you open the administration tool, you can reach the security manager by the Menu :
Manage > Security