With standard relationship or edge expansions, you can traverse one relationship at a time and see all the objects related to the starting node through instances of that one relationship. For example, you might expand an area to view the documents. From there, you can then find the document type related to that document. However, when you expand with grouping, you can use one expansion operation to expand an area to see all the documents, grouped beneath their corresponding document type — effectively expanding two standard relationships at once.
The expanded items are given structure so that it is clear to which document type each document in the expanded list is linked. Counts are appended in brackets to indicate the number of documents for each area that are organized within each document type. This method of expansion by grouping supports up to two grouping levels.
For more information about creating drill down items that group items, see DrilldownByGrouping client API.