BW Star Schema - SAP BW

we introduced the concept of a star schema.
What does the InfoCube data model look like at the database level?

In this we will explore the relationships between database tables. They will give us a clear idea of what the star schema looks like in BW. Again,we use a step-by-step procedure.

Work Instructions:
Step 1. Run transaction SE11,enter /BIC/FIC_DEMOBC as the fact table name,and then click Display.

Note:From Screen,we know that /BIC/FIC_DEMOBC is the name of the fact table.
If we are interested in only the table contents,and not the table definition,we can run transaction SE16 instead.
ABAP Dictionary: Intial screen

Step 2. The Check table column lists parent tables of the fact table. Double-click /BIC/DIC_DEMOBC3 to display the sales representative dimension table.

Note:BW uses </BIC/|/BIO/>D <InfoCube name><Number starting from 1> to name dimension tables.

  • </BIC/|/BIO/>D<InfoCube name>P is for the data packet dimension. We will discuss its role in BW.
  • </BIC/|/BIO/>D<InfoCube name>T is for the time dimension.
  • </BIC/|/BIO/>D<InfoCube name>U is for the unit dimension.

Dictionary display table

Step 3. The dimension table does not have any check tables,but it has a field called SID_IO_SREP. Click boxto display the table's contents.
Dictionary display tables

Step 4. ClickClick to execute.
data Browser : table

Step 5. Notice that SID_IO_SREP 11 corresponds to DIMID 23.From Screen, we know that DIMID 23 is the value of the field KEY_IC_DEMOBC3 in the first row of the table /BIC/FIC_DEMOBC.Then what does SID_IO_SREP 11 represent?
data Browser

Step 6. Repeat Step 1 to display the contents of IO_SREP's SID table,/BIC/SIO_SREP. This screen shows the SID table definition. Clickbox to display the table's contents.
to display the table's contents.

Note:Here SID is Surrogate-ID,not the System ID used to name an SAP system.BW uses </BIC/|/BIO/>S<characteristic name> to name a characteristic's SID table.

Step 7. The contents of the SID table /BIC/SIO_SREP are displayed.
In this screen,we see that SID 11 corresponds to SREP01,a sales representative ID in the first record of Table.
data Browser table /BIC/SIO_SREP select Entries

Following the same approach,we can discover the relationships between the SID table /BIC/SIO_SREP,the master data table /BIC/PIO_SREP,and the text table /BIC/TIO_SREP. The contents of the latter two tables are shown in Screens

Step 8. Repeat Step 1 to display the contents of IO_SREP's master data table,/BIC/PIO_SREP. This screen shows the table's contents.
Data browser table

Step 9. Repeat Step 1 to display the contents of IO_SREP's text table,/BIC/TIO_SREP. Screenshows the table's contents.
Data browser table

Step 10. Repeat Step 1 to display the contents of IO_SREP's hierarchy table,/BIC/HIO_SREP. Screen shows the table's contents.

Note:Screen shows the contents of the hierarchy table,/BIC/HIO_SREP. Unlike the master data table and the text table,the hierarchy table does not link to the SID table. BW builds the hierarchy based on the information in the tables /BIC/IIO_SREP,/BIC/KIO_SREP,and /BIC/SIO_SREP.
SCREEN 7.10
Data browser table

Result:
Based on our discussion,we can draw a simplified star schema as shown in Figure.
BW STAR SCHEMA FOR PART I INFOCUBE DESIGN
BW STAR SCHEMA FOR PART I INFOCUBE DESIGN

The solid lines are the true master–detail relationships,reinforced by foreign keys. The dashed lines are relationships that are maintained by ABAP programs,but not reinforced by foreign keys.

The dashed-line relationships allow us to load transaction data even when the database does not contain any master data. Screen shows the InfoPackage used Under the Update parameters tab,notice the Always update data,even if no master data exists for the data option.
Administrator workbench Modelling

With this star schema in mind,let's look at three InfoCube design alternatives.


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