Each data source includes
one or more standard data items. You decide which data items to use
to define a query for a report section. You can use all the data items
in the data source or a subset of data items. Each standard data item
is classified as either a category, a hierarchy, or a measure.
Category
A data item whose distinct
values are used to group and aggregate measures. There are four types
of categories: alphanumeric, date, timestamp, and time. Alphanumeric
categories can be made up of all letters, all digits, or a combination
of the two. Categories that have values that are all digits might
be physically stored as character or numeric data. The data type affects
how values are handled in relation to some functionality, such as
filtering, sorting, and formatting.
Examples of alphanumeric
categories include data items such as
Product ID
,
Country
,
Employee
Number
, and
Employee Name
.
Date, timestamp, and time category examples are
Order
Year
,
Date of Sale
,
and
Delivery Time
.
Measure
A data item whose values
can be used in computations. Usually, these values are numeric. Examples
of measures include Sales Revenue
, Units
Sold
, and Salary
.
The default format
of a measure is specified by the data source that contains it. You
can modify the format of some measures.
Every measure has a
default aggregation method, which is specified by the data source
that contains it. In some cases, you can change the method. However,
if you use a measure as part of a custom data item, then the measure
is always calculated by using the default aggregation method.
Hierarchy
An arrangement of the
levels in a dimension from general to specific. The first level in
the hierarchy is the root level.
For example, a common
dimension in a multidimensional data source is
Time
.
A dimension that is named
Time
might
have a hierarchy named
YrQtrMth
. Such
a hierarchy might enable you to look at data for each
Year
(the
root level), drill down to see the data for each
Quarter
(second
level) in a specific year, and then drill down to see the data for
the three
Months
(third level) that
make up a particular quarter.
Hierarchies are available
only in multidimensional data sources.