Some operations in DQC are based on certain record groupings. These operations then need to hold complete groups of records. This involves the need to preserve all historical data to allow the collection of whole groups when only part of them comes to the input. The storage for the historical data is called the Repository.

This step retrieves historical records and forms groups of them from the repository, as well as storing them back. Moreover, this service manages coordination between several process running in parallel and ensures logical integrity of record groups concurrently updated in the repository.

Supported operations are:

• Unification
• Group classification
• Group representatives creation
• General expression evaluating and assigning (not technically a group operation, but can be usable in cooperation with others)