5 Data Warehouse projects
3. Make sure that the Start New Star Schema Wizard check box is selected (the default) and
then click OK. The New Star Schema wizard opens.
4. Provide a name and description (optional) for the star schema.
5. Select one of the available fact types:
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Transactional - A star schema with a transactional fact table allows you to retrieve
the desired data, even if a dimension table contains multiple versions of the same
record. To use an example from the automotive industry, selecting "OrderDate" as the
Transaction Date would allow you to generate a report for the number of customers
who bought cars in New York between 2013 and 2016, even if a customer moved to a
different city (which would also result in a new record being added to the Customers
dimension).
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Aggregated - A star schema with an aggregated fact table allows you to make
aggregate calculations based on the fact table attributes. For instance, you could
create an aggregated fact that shows the total freight costs per shipping region and
product category. Additionally, the presence of a transaction date in the fact table
makes it possible to retrieve the desired data, even if a dimension contains multiple
versions of the same record. To use an example from the shipping industry, a shipper
could use an aggregated fact to generate a report for the total cost of shipping rice to
Australia from 2015-2016.
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State Oriented - A star schema with a state oriented fact supports Type 2 columns in
the fact table. This is useful in cases where the fact is not a singular event in time, but
rather, consists of multiple "states" or events that occur over time. Typical example of
facts with multiple states are insurance claims or flight reservations. There are also
cases when the same entity is treated as both a fact and a dimension - for example,
Customers. In such cases, a report could be generated that relates to the state of the
fact, such as the time a claim was submitted to the time it was approved.
6. Click Next.
7. In the Facts screen, choose one fact for the star schema and then click Next. The
Dimensions screen is displayed. The left pane lists the dimensions that can be selected
while the right pane displays a diagram of the star schema with the selected dimensions. You
can view a dimension’s lineage by selecting the desired dimension and then clicking the
Lineage button. For more information on lineage, see
Lineage and impact analysis (page
179)
.
The left pane of the Dimensions screen contains the following areas:
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Existing Dimensions - Lists the dimensions that already exist in your data mart. Note
that only dimensions that are relevant to the selected fact table will be displayed.
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Create New Dimensions - Lists all of the dimensions that can be added to the star
schema.
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Date Dimensions - Lists all of the Date dimensions that can be added to the star
schema. Note that these dimensions will only be available for selection if you added
the Date and Time entities to your model. For an explanation of how to do this, see
Adding Date and Time entities to your model (page 180)
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