Track Changes In A Measure Over Several Time Periods - IBM Cognos User Manual

period will be reported, and the corresponding offsets, to track values that
apply to a period other than the current one.
For more information about specifying custom time periods, see "Track
Changes in a Measure over Several Time Periods" and "Track Changes in a
Measure in Future Time Periods" on page 84.

Track Changes in a Measure over Several Time Periods

In some cases, you may want to set up relative time categories that span several
specific time periods, at points in the past or the future. Several built-in relative
time categories are available, to help or, if you have an unusual reporting period
not covered by the automatically created relative time categories, you can create a
custom category.
For example, suppose your users want to use relative time categories to track sales
for prior months, quarters, and years. However, some users also want to track
sales over six-month periods prior to the current date, in both the current year and
the previous year. You set up an N-period running total category that spans the
six months leading up to the current month, this year, and last year. Your OLAP
report users can now analyze growth trends for the required time periods.
If you enter positive numbers for either the Target offset or the Context offset,
your model must include source columns with time periods later than the current
period, as positive values in these fields signal measures that are essentially
forecasts, in future time periods.
Procedure
1. Open the Categories diagram for the time dimension and position the pointer
over the right side of the root category.
The pointer changes to a crosshair.
2. Drag the pointer to the right of the root category.
A new relative time category is created and its property sheet opens.
3. In the Category code box, type a meaningful name for the new category, such
as Previous 6 Months.
4. Click the Relative Time tab.
5. In the Relative time box, select Custom.
6. In the Basic approach box, select N-Period Running Total or N-Period
Running Total (Grouped).
Grouped lets you easily create a series of categories spanning different ranges
of time.
7. In the Number of periods box, type the number of periods to include.
For example, if you are creating a 6-month running total, type the number 6.
8. In the Target period box, select the type of period for which the N-period
running total will be kept.
For example, if you are creating a 6-month running total, select Month.
9. In the Target offset box, type a number that reflects an offset for the Target
period relative to the current period.
For example, if the current period is December 2006 and you want a 6-month
running total up to (ending) November 2006, type -1.
10. In the Context period box, select a time period one or more levels higher than
the Target period, within which you want to calculate the N-period running
total.
Chapter 4. Structuring Your Data Into Dimensions
83