Database Reference
In-Depth Information
Many of the preceding objects, which you create in your data model, are equivalent
to objects that are created by the wizard, such as a Currency and Time dimension, or
an Exchange Rate measure group. There are also other important concepts to learn
before using the wizard.
The Exchange Rate measure group contains the exchange rates for converting
many different currencies to a single reference currency that we will call the
Pivot Currency
. For example, consider the following table:
Date
Currency
Rate
2009-02-06
EUR
1.2871
2009-02-05
EUR
1.2835
2009-02-06
CHF
0.8550
2009-02-05
CHF
0.8578
The
Rate
column here contains the exchange rate between the currency in the
Currency
column and the US Dollar (USD). In this case, the Pivot Currency is USD.
Note that the Pivot Currency is not an attribute of the preceding table and the use of
USD is implicit.
The measures that have to be converted using the Currency wizard store their values
in a
Local Currency
. The local currency can be identified directly (for example, when
the Currency dimension is directly related to the measure group) or indirectly (for
example, when it is defined as an attribute of another dimension with a regular
relationship to the measure group, such as the Country of a Customer). When data
is collected in just one currency, the Local Currency will always be the same. In this
case, making the Local Currency the same as the Pivot Currency is a good idea, just
to make the conversion process more linear and easier to debug.
Finally, we will refer to the currency that users want to display data in as the
Reporting Currency
. It will be a member that the end user selects from the Reporting
Currency Dimension, a dimension which will be created by the wizard and which
will contain all the possible values for the Reporting Currency. This dimension will
be based on a named query defined in the Data Source View, which in turn queries
the main table of the Currency dimension.
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