If you have parent or child hierarchies of configuration items or issues, you can now recursively define dependencies between parent field values and the appropriate child field values. If, for example, you wish to ensure that a parent issue is not closed until all the child-issues (children) are closed, you can manage this dependency using one of the distribution rules defined in this document. Similarly, if you wish to define the parent issue's Spent Hours as the sum of the children's Spent Hours you can define this aggregation rule, too.

Parent field value updates can be recursively distributed to children and child field values can be recursively aggregated into parent field values.

This is controlled in the distribution and aggregation rules shown in Tracker > Configure > Fields for each applicable field:

The set of applicable distribution and aggregation rules for a field depends on the field and its type.