An aggregate is a materialized, aggregated view of the data in an InfoCube. In an aggregate, the dataset of an InfoCube is saved redundantly and persistently in a consolidated form on the database.
Aggregates allow quick access to InfoCube data during reporting. Similar to database indexes, they serve to improve performance.
Aggregates are particularly useful in the following cases:
Executing and navigating in query data leads to delays if you have a group of queries
You want to speed up the execution and navigation of a specific query
You often use attributes in queries
You want to speed up reporting with characteristic hierarchies by aggregating specific hierarchy levels
An aggregate is made up of the characteristics and navigation attributes that belong to an InfoCube. Characteristics that are not used in the aggregate are compressed.
Each component of an aggregate has to be assigned to a selection type. A selection type indicates the degree of detail to which the data in the underlying InfoCube is aggregated. You can choose one of the following selection types:
All characteristic values ("*"): The data is grouped by all values of the characteristic or navigation attributes (see Selection Type "All Characteristic Values" ('*')).
Hierarchy level (H): The data is grouped by the hierarchy level node. You can also store values on the hierarchy levels of an external hierarchy (see Selection Type "Hierarchy Level" ('H'))
Fixed value ("F"): The data is filtered by a single value (see Selection Type "Fixed Value" ('F')).
You can use both time-dependent attributes and time-dependent hierarchies in aggregates.
Access to Aggregates During Reporting
If you have created an aggregate for an InfoCube, activated it and entered data for it, the OLAP processor can access these aggregates automatically. For more information about the order in which the OLAP processor accesses the aggregates, see Performance Optimization with Aggregates. The different results are consistent when you navigate in the BEx query. The aggregate is transparent for the user.
System Response Upon Changes to Data
New data is loaded to an aggregate at a defined time using logical data packages (requests). After this operation (roll up), the new data is available in reporting (see System Response Upon Changes to Master Data and Hierarchies)
" Performance Tuning for Queries with BW Aggregates" in SAP Service Marketplace on the SAP Business Warehouse performance page.