IBM Cognos User Manual page 364

Model query subjects are extracted using the same mechanism by which queries
are executed within IBM Cognos. Therefore, the Extract Size property has no effect
on the query execution.
Measure Dimensions
When extracting a measure dimension, you should create a model query subject
containing the measures that you want. You should include the business key query
item from each of the levels of each dimension, depending on the level of
granularity that you are trying to achieve.
For information about externalizing model query subjects, see "Framework
Manager Considerations" on page 352.
Characteristic Dimensions
Characteristic dimensions are externalized independent of the type of SAP BW
data source, such as InfoCube or SAP BW query.
Framework Manager uses a single approach to externalize all dimensions that do
not contain fact query items. In these cases, the extract size configuration setting is
used to control the manner in which data is extracted from SAP BW.
Note: Model query subjects are externalized in a different manner, regardless of
whether they contain fact query items or not. For information about externalizing
model query subjects, see "Framework Manager Considerations" on page 352.
Key Figures Dimensions from an SAP BW InfoCube
When externalizing the key figures dimension from a model based on an InfoCube,
Framework Manager uses exactly the same approach as used for externalizing
model query subjects.
For an InfoCube containing more than a few thousand transactions, externalizing
an InfoCube directly from Framework Manager can easily exceed both time and
memory limits on either the client or server. In such cases, it is highly
recommended that an SAP BW query be used as the basis for externalizing the
SAP BW metadata.
Key Figures Dimensions from an SAP BW Query
Using a BEx query as the basis for externalizing key figures from an SAP BW data
source is, in most cases, the best approach. By using a BEx variable to break the
data of the key figure dimension into manageable sections, arbitrarily large
volumes of transaction data can be extracted from SAP BW.
Note, however, that this approach incurs some restrictions as to what can be
extracted from SAP BW, and how it can be extracted. The remainder of this section
describes how an SAP BW query is used to extract data from SAP BW, including
all known restrictions and limitations.
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IBM Cognos Transformer Version 10.1.1: User Guide