Creating The Time Dimension - IBM Cognos User Manual

You are required to specify both the date source column and the Dimension name
for your time dimension. You can insert manual levels into a time dimension, but
you must specify a date function for each level so Cognos Transformer knows how
to relate the categories to their parent levels during category generation.
For example, suppose you insert the manual level Half Year between the source
levels Quarter and Year. After adding the two required categories to your new
level, you must also remember to connect Q1 and Q2 to the first half, and Q3 and
Q4 to the second half. Otherwise your time categories will not generate properly.
If the standard date functions do not meet your users' needs, you can manually
create a custom time dimension. For example, you can add irregular work shifts or
handle time-related data that comes from more than one source column. You can
mix levels that use date functions with levels that derive their categories entirely
from other source columns, such as Sales Promotions for a time period. However,
these non-date levels will not be generated if you use the Generate Date
Categories command on the Run menu.
You cannot import a time dimension from another OLAP data source. You must
use a date field as the source for your time dimension instead.
Note: If there is a null value in the date column, an invalid date category is
generated. To avoid this problem, suppress this category so that it does not appear
in the cube "Omit Categories Using Suppress" on page 134, or clean the data to
eliminate the null value.

Creating the Time Dimension

Create a time dimension using any of several methods. Whichever method you
choose, you must define or confirm the date input format. You may discover that
some of your data sources include information about their columns (sometimes
called metadata), while others do not. Cognos Transformer requires information
about how dates are formatted in order to correctly interpret them.
To create a time dimension, you can use any of the following methods:
v Use the Date Wizard.
Cognos Transformer prompts you for information about the time dimension and
then creates the dimension for you.
v Manually create a new time dimension and then successively drag the required
date columns to each level in the dimension.
Set the appropriate date function and other date-related properties for each level.
v Drag the time dimension source category from the Data Sources list to the
Dimension Map.
Note: The Data class of the time dimension source category must be set to Date.
This automatically creates a time dimension with the standard levels Year,
Quarter, and Month.
v Design the dimension before you have any items in the Data Sources list.
Insert a new dimension, setting the Dimension type to Time. Click the Time tab
on the Dimension property sheet, and you are prompted to specify the source
column containing the dates for your new time dimension in the Date Level
Creation dialog box. Click OK twice, and from the Run menu, click Generate
Date Categories.
Chapter 4. Structuring Your Data Into Dimensions
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