Data sets are created by extracting data from packages or data modules. Data sets can be used to gather a customized collection of items that you use frequently. As you make updates to your data set, dashboards and stories that use the data set are also kept up to date the next time you open them.
You define a data set by choosing one or more items (columns) from a package or data module, and apply filters to reduce the data. You’re essentially specifying the rectangle of columns and rows of data that you need. The data is extracted and stored within the Cognos® Analytics system.
Data sets can improve query performance and reduce the workload on your databases. The following are some reasons for using data sets:
- Improve query performance if your database is slow.
- Reduce the load on an overworked database (especially during peak periods).
- Retain a version of the data at a specific time.
For data sets created from relational packages or data modules, you have the option Summarize detailed values, suppressing duplicates. When you use this option, measure values are aggregated to the lowest grain that is explicitly included in the data set. For example, your data warehouse stores millions of records pertaining to each transaction where units were sold, but you’re only interested in analyzing the total sales per region. If your data set contains only the Region and Units Sold columns, and you use this option, the data set will contain only as many rows as there are regions.
For more information, see data sets and best practices for improving query performance on uploaded files and data sets.