IBM BPM - What is the Performance Data Warehouse ?

Here's an introduction to PDW from Neil Kolban: -

The Performance Data Warehouse is a database responsible for collecting and managing data originated by Process Server instances. Think of this as the repository for information about the history of the system as is used for reporting of the outcome of processes. The sourcing of data for reporting comes from the single Performance Data Warehouse database which may be associated with multiple Process Server instances. This architecture allows aggregation of information from multiple servers to be achieved. Since generation of reporting knowledge can be computationally expensive, the separation of the Process Servers from the Performance Data Warehouse also allows for reports to be generated without impacting the operation of running processes.

and here's what the BPM documentation says: -

In Process Designer, define the variables that you want to track and then send tracking definitions to the Business Performance Data Warehouse.

The Business Performance Data Warehouse creates a database table to hold the tracked data.

Run instances of your processes on the Process Center Server or a Process Server in a runtime environment.

The Business Performance Data Warehouse retrieves tracked data for each variable from the Process Center Server or Process Server at regular intervals.

Create reports in the Designer that query the Performance Data Warehouse to retrieve the required data.

Reports that you define in the Designer display as scoreboards in Process Portal or a customized portal.

You can also query the Performance Data Warehouse from third-party tools like Microsoft Access to generate reports.

Source: How reporting works in IBM BPM

This may also be of use: -

Reporting options

Determining which reporting option meets your needs