In order to cover the re-alignment of master data attributes, the master data tables in a BI Data model are not linked directly to Info Cubes ( but connected via Surrogate Keys ) as the following, simplified, picture below explains:
As you can see, pointer or translation tables called SID (Surrogate-ID) tables are used in the BI data model to link the master tables of the BI data model to Info Cubes.
The above graphic shows a simplified version of what types of SID tables exist .
SID Tables
SID tables play an important role in linking the data warehouse information structures to the InfoCubes and Data Store Objects. To speed up access to InfoCubes and DataStore Objects and to allow an independent master data layers, each characteristic and attribute is assigned a SID column and their values are encoded into 4-byte integer values.
InfoObject definition and SID tables
To offer optimal performance with the various data models with respect to master data access, three different SID tables might be generated.
SID tables with respect to master data:
- The SID table is always generated if an InfoObject is not defined as ‘attribute only’ (tab page general).This table is used if the access to an Infocube or DataStore Object uses a navigational attribute or if the access is via a characteristic without attributes. Name of the table: /BIC/S
- The non-time dependent attribute SID table of a characteristic for access via non-time dependent attributes. Name of the table: /BIC/X
- The time dependent attribute SID table of a characteristic for access via time dependent attributes.Name of the table: /BIC/Y
All these SID tables are automatically maintained during master data load. SID tables are also maintained
during InfoCube load if no referential integrity check is enforced (InfoPackage).
But in case of Line Item Dimension the SID table acts as a Dimension Tables, that means NO Dimension table is created for this .
Dimensions with only one characteristic (line item dimensions)
It is very often possible in this model to assign only one characteristic to a dimension.This will probably occur with specific reporting requirements or if for example you have the document line item in your model which occupies lot of space of Fact table. In these situations a dimension table means only overhead. BI allows you define this kind of dimension as a line item dimension (Check box dimension definition while creation of Info cube). In doing this no dimension table will be generated for this dimension. As dimension table will serve the SID table of this characteristic. The key in the fact table will be the SID of the SID Table.
pictures explains
But in case of Line Item Dimension the SID table acts as a Dimension Tables, that means NO Dimension table is created for this .
Dimensions with only one characteristic (line item dimensions)
It is very often possible in this model to assign only one characteristic to a dimension.This will probably occur with specific reporting requirements or if for example you have the document line item in your model which occupies lot of space of Fact table. In these situations a dimension table means only overhead. BI allows you define this kind of dimension as a line item dimension (Check box dimension definition while creation of Info cube). In doing this no dimension table will be generated for this dimension. As dimension table will serve the SID table of this characteristic. The key in the fact table will be the SID of the SID Table.
pictures explains
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