What is aggregation?
Covers the main concepts behind aggregation to assist you in understanding how your report definition selections affect the aggregated totals in your reports.
In the Tivoli® Netcool® Performance Manager software, aggregation is the grouping of values and then applying an algebraic expression to the grouped set of values.
Example: Applying an Aggregation Type
sum(2,3,4) = 9In the above example, we have applied the sum aggregation type to the grouped field values 2, 3 and 4. The grouped field values are also known as the arguments of the sum function.
TheTivoli Netcool Performance Manager software uses a number of aggregation types in addition to sum for calculating aggregation. The aggregation type determines how to calculate (aggregate) rolled-up field values over time and over element. Aggregating over time occurs when the Group By option in the report definition is set to Attribute and Time, and aggregating over element Time and Attribute. See Aggregation types for a description of the different aggregation types.
In the Tivoli Netcool Performance Manager software, aggregation generally occurs when the grouped field values are roll ups; that is, rolled-up fields. There are a number of roll-up types: aggregation of descendants, aggregation of time and element, and aggregation of element and time.
The context of a roll-up determines which arguments are used in the function.
Example of the Importance of Context
This example consists of the following data for the Peg2 field of the Antenna entity, and two algebraic expressions.
| Entity Instance | Peg2 |
|---|---|
Cell_1
Antenna
hr 01 hr 02 hr 03 |
3
6 9 |
Cell_2
Antenna
hr 01 hr 02 hr 03 |
17
19 21 |
A. sum(Cell_1.Antenna.Peg2)
B. sum(Cell.Antenna.Peg2)Expression A would be executed as follows:
sum(3,6,9) = 18In this expression, the arguments consist of the Peg2 values for the antenna of Cell_1. The Peg2 values are rolled up to provide the single total of 18 for Cell_1.
Expression B would be executed as follows:
sum(3,6,9,17,19,21) = 75In this expression, the arguments consist of the Peg2 values for all cell antennas. All the Peg2 values for all the antennas have been rolled up to yield the single total of 75 for the entity Cell.
The concept of roll ups and aggregation are further explored in the topic Aggregation of descendents.