Best Practices for SAP BI using DB2 9 for z/OS - IBM Redbooks

Activating and filling
In order to use an aggregate in the first place, it must be defined, activated, and
filled. When activated, the required tables are created in the database from the
aggregate definition. Technically speaking, an aggregate is actually a separate
BasicCube with its own fact table and dimension tables. However, aggregates
might share the dimension tables of the corresponding InfoCube if those tables
have the appropriate structure.
Upon creation, every aggregate is assigned a technical name, which is a unique
number consisting of six digits where the first digit is always set to 1. The table
names that make up the logical object that is the aggregate are then derived in a
similar manner, as are the table names of an InfoCube.
For example, if the aggregate has the technical name 100001, the E- fact tables
have the following names: /BIC/E100001 and /BIC/F100001. Its dimensions,
which are not the same as those in the InfoCube, have table names such as
/BIC/D100001P, /BIC/D100001T, and so on.
When you fill an aggregate, you load it with data. This action can only be
triggered from the aggregate maintenance. Also note that an aggregate can be
filled from the data of a larger aggregate that is already filled. This means that
very highly summarized aggregates, as a rule, can quickly obtain data from other
aggregates. In contrast, it can take a long time to build aggregates from the
InfoCube.
Because of this, all aggregates are filled in background processes. If there are
several aggregates scheduled to be filled in one process, a hierarchy sequence
for the aggregates is determined first, and it is then processed sequentially. This
guarantees that very highly summarized aggregates are built from the more
detailed aggregates.
Roll-up
If aggregates are defined, new data packets that are loaded into the InfoCube
cannot be used for reporting until they are written to the aggregates by a roll-up.
During this process you can continue to report using the data that existed prior to
the recent data load.
There are three different options for rolling up data:
► You can set up the InfoCube so that every data packet is automatically rolled
up into the aggregate if it is technically correct and the quality has been
ensured.
► The roll-up can be also started manually from the Administrator Workbench.
This is appropriate if the data of several packets form a logical unit and are
only valid if they are released together.
Chapter 12. Concepts, activities, and terminology 271