IBM Cognos User Manual page 355

v If you include a free characteristic, no values will appear for that
characteristic in the key figures extract. A filter on a free characteristic acts as
a filter on the returned SAP BW data. You can use this as a filter to define a
subset of an InfoCube.
v Use a picklist prompt, rather than a type-in prompt for the query. A picklist
prompt provides values for segmenting the data.
5. To define the metadata that will populate the Cognos Transformer cube, you
must change the properties of each characteristic that you have selected for
inclusion. Right-click a characteristic, and select Properties.
6. In the Properties of Characteristic dialog box, change the Display As value to
Key, and the Suppress Results Rows value to Always. Note that any
restriction or filter applied here will be carried forward in Cognos Transformer.
7. Repeat steps 5 and 6 for each characteristic that you selected in step 4.
Note: You should only select the characteristics that you require. To avoid
excessive memory consumption, and decreased system performance or failure,
carefully consider what characteristics you want to include in the query. We
recommend that you consult an SAP BW administrator to ensure that the data
volumes are not exceeded.
8. Click the Queries Properties icon, and in the Extended tab select the Allow
External Access to this Query check box. This exposes the query to Framework
Manager.
9. Click Save, and provide the new query with a Description and a Technical
Name. We recommend that you use the SAP BW naming convention in the
Technical Name field. That is, begin the entry with the letter 'Z' followed by an
intuitive name or your standard naming convention. It is important to write
down this technical name, as you will need it to find the query in Framework
Manager.
Results
You are now ready to create a variable "Create a Variable." For more information
on using the SAP Query Designer, see your SAP BW documentation.
Create a Variable
You must now create an optional prompt parameter for the query so Cognos
Transformer can issue smaller queries to SAP, and thereby retrieve the entire data
set.
There are no set rules for variable usage when extracting SAP BW data for use in
Cognos Transformer. However, you must be careful not to request too much data
that could potentially perform poorly or error out with out-of-memory messages
within your SAP environment.
A basic guideline to follow is that when a variable is utilized for the extraction,
Cognos Transformer will first fetch all members that exist for the dimension
against which the variable is defined. After this, Cognos Transformer will perform
individual data fetches to extract the fact data for each of the individual members
within the dimension in order to satisfy the variable.
This allows Cognos Transformer to break down your data extraction into
manageable chunks that the SAP BW server can handle. There are no set standards
as to which dimension to apply it to. To achieve optimal performance, you must
understand your SAP BW data and determine which dimension evenly breaks up
the factual data.
Appendix E. Guidelines for Working with SAP BW Data for Use in Transformer
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