SAP BW Extended Multidimensional Data Model

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In a traditional star schema model, the reference data is modeled in dimensions and limited to one cube only. In SAP BW, the reference data is shared across all InfoCubes and ODS objects. This is managed via an intermediate table, called a Set ID (SID) table. The SID table connects attributes of a dimension to a corresponding set of master data, text, and hierarchies, as shown in Figure 12-4.

Figure 12-4: Extended Star Schema for SAP BW 1.2B InfoCubes.

Data access takes more resources; however, due to additional joins to access reference data, this model is very flexible and can share reference data across the entire data warehouse, regardless of where reporting is done-against an InfoCube, ODS, or other data objects.

Note 

In SAP BW 2.0, the SID tables are further decomposed into two separate SID tables: one for time-dependent and another for time-independent attributes of reference data objects. This makes it easier to implement and manage time-dependent dimensions, known as slowly changing dimensions. To implement slowly changing dimensions, master data must be implemented as time dependent. Then at query run time, use a variable to pass the time period of choice for the relevant master data attributes, as discussed in Chapter 11.

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