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

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SID Table<br />

SID Table<br />

SID Table<br />

An InfoCube is represented in the database as a set of relational tables, as<br />

shown in Figure 12-5. These are arranged according to the star schema, a<br />

technique that organizes data in terms of data facts and business dimensions.<br />

Master<br />

Hierarchies Text<br />

Master<br />

Hierarchies Text<br />

Master<br />

Hierarchies Text<br />

SID Table<br />

Figure 12-5 Extended star schema<br />

Hierarchies Text<br />

dimension<br />

dimension<br />

SID Table<br />

Master<br />

Hierarchies Text<br />

dimension<br />

Master<br />

Fact<br />

SID Table<br />

Hierarchies Text<br />

dimension<br />

SID Table<br />

Master<br />

dimension<br />

Master<br />

Hierarchies Text<br />

SID Table<br />

Hierarchies Text<br />

SID Table<br />

SID Table<br />

Master<br />

Hierarchies Text<br />

Master<br />

Hierarchies Text<br />

SID Table<br />

Master<br />

Master<br />

Hierarchies Text<br />

The star schema places several dimension tables around a central fact table.<br />

The E- fact table stores key figures, while the surrounding dimension tables store<br />

the characteristics needed <strong>for</strong> evaluating and reporting on those key figures. fact<br />

tables are the largest tables in star schemas, and they may contain billions of<br />

entries.<br />

Dimension tables are independent of each other. The E- fact table links the<br />

dimension tables and the key figures. To link these tables, dimension identifiers<br />

are used. A dimension identifier uniquely identifies a particular combination of<br />

characteristic values in a dimension table, <strong>for</strong> example, a certain product and the<br />

corresponding product group. Characteristics that are correlated, such as<br />

product and product group, are usually put in the same dimension.<br />

Chapter 12. Concepts, activities, and terminology 265

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