Business Information Warehouse for SAP (Prima Techs SAP Book Series)
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.
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. |
| Team-Fly |