Extended Star Schema
Many of the problems associated with the basic star schema are resolved with the BW extended star schema. With the extended star schema, attributes are removed from the dimensions and placed outside the InfoCube in master data tables. 
The BW extended star schema differs from the basic star schema. It is divided by a solution dependent part (InfoCube) and a solution independent part (attribute, text and hierarchy tables) which is shared among other InfoCubes.In BW, attributes located in the dimensions are called characteristics. In BW, attributes located in a master data table of a characteristic are called attributes of the characteristic. When designing a solution, it is a great challenge to decide whether an attribute should reside in a dimension table and thus in the InfoCube or in a master table or even both. Data is loaded separately into the master data (attributes), text and hierarchy tables. The SID table provides the link between the master data and the dimension tables.
The fact table and the relevant dimension tables of an InfoCube are connected with one another relationally using the dimension keys. The dimension key is provided by the system per characteristic combination in a dimension table.
With the execution of a query the OLAP processor checks the dimension tables of the InfoCube to be evaluated for the characteristic combinations required in the selection.
The dimension keys determined in this way point the way to the information in the fact table. Dimension tables consist of a maximum of 248 characteristics. The Time dimension holds the time characteristics needed for analysis. The Unit dimension contains the unit of measure and currency characteristics needed to describe the key figures properly. The Data Packet dimension is used to identify discrete packets of information loaded into the InfoCube. In this way, packets can be deleted, reloaded or maintained individually.
6 Responses to Extended Star Schema
That was a very good, concise definition. Thank you.
Michael
This is the best and clearest description of InfoObjects and InfoCube extended star schema I have come across! Even the SAP training manuals are not clear about the relations between Characteristics, Master Data, Attributes, Texts and Hierarchies :-(
Keep it up!
Good explanation of the extended star schema.
Rakki
very good explanation.
Can you elaborate more on how the linking between the Master Data tables and the Dimension table happens. As you said "The dimension key is provided by the system per characteristic combination in a dimension table", is the SID also generated for each combination of the master data?
I am able to understand the link between the fact table and the dimension table, but not between the dimension table and the master data table.
Sumanth,
Dimension table contains Dimension id and SID's of each characteristic in the dimension.
Eg: if a dimension contains 2 characteristics "Credit Control Area" and "Customer number" then dimension table contains one dim id and 2 SID's of each characteristic.
Table Structure:
Dim ID | SID(CCA) | SID (Customer)
Check at dimension tables at TCode: SE11.
Hope it helps
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