IBM Cognos User Manual page 347

Time state rollup
option Results in reporting component
First Period Shows the measure value from the first subordinate period in the time
period being examined. For example, a time dimension contains years,
quarters, and months, and you are examining data at the quarter level.
For each quarter, the First Period option reports the measure value
from the first month of the quarter. When you examine data at the
year level, the option reports the first value from the first month in the
first quarter of each year.
Last Period Shows the measure value from the last subordinate period in the time
period being examined. For example, if a time dimension contains
years, quarters, and months, and you are examining data at the quarter
level, for each quarter, the Last Period option reports the measure
value from the last month of each quarter. When you examine data at
the year level, reports the value from the last month in the last quarter
of each year.
Current Period Shows the measure value from the category that is designated as the
current period in the time dimension. If the time period being
examined does not include the current period, the result is identical to
Last Period. For example, a time dimension contains years, quarters,
and months, and Quarter 1 starts in January. The current period is set
to April 2007. At the year level, the Current Period option reports the
measure value for April 2007. At the quarter level, the option reports
the measure value for April in Quarter 2 because April is the current
period, but it shows the value of the last active month in every other
quarter; that is, March for Quarter 1, September for Quarter 3, and
December for Quarter 4.
Average Shows the average of the measure values from all categories in the
time period being examined.
Duplicates Rollup
The following table lists the available duplicates rollup options and explains how
the results appear in the reporting components.
Duplicates rollup
option Results in reporting component
None (regular Uses the Regular Rollup function specified for the measure.
rollup)
Sum Sums the measure values found in the duplicate records, except for
external rollups, which override this function.
Minimum Takes the smallest of all values for the measure found in the duplicate
records.
Maximum Takes the largest of all values for the measure found in the duplicate
records.
Average Takes the average of all values for the measure found in the duplicate
records. If the Regular Rollup option is also set to Average, duplicates
rollup is performed before regular rollup.
Takes the first value of all values for the measure found in the
First
duplicate records by using the order of the records in the data source.
Last Takes the last value of all values for the measure found in the
duplicate records by using the order of the records in the data source.
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Appendix D. Reference