# Risk Type Hierarchy
The following outlines some general concepts about Risk Types.
# Risk Types have parents
Almost every Risk Type has a parent. The only Risk Type without a parent is called the root Risk Type. Multiple Risk Types can have the same parent. These sub-Risk Types are considered the parent's children.
Each child Risk Type can also be a parent to other Risk Types.
Here is a full example of a Line that has Risk Types which nest three levels deep below the root Risk Type. This is the maximum level of depth that can be added to the Risk Type hierarchy.
+-- Policy (root) | +-- Office Complex | +-- Office Building | +-- Department | +-- Storage Building
This structure allows us to do things like set premium all the way at the individual Department level, then accumulate that premium for each Office Building, each Office Complex, and finally for the Policy as a whole.
# Risk Types can reference ancestor rating information
Risk Types have access to individual rating information (data fields, rate tables, and shared calculations) on any of their ancestors. For example, a "Fire Factor" Rate Table on the Office Building referencing a "Distance to Fire Station" Data Field on the Office Complex.
# Risk Types can only reference children in aggregate
Risk Types can only look down at their children's data in aggregate. For instance, a sum or average of data across all children.
This restriction is in place because Risk Types will have multiple instances of their children and it would be difficult for calculations to specify which instance they are retrieving data from.
For example, the Office Complex Risk Type could count the number of Office Buildings on the quote and provide a discount. Or the Policy Risk Type could receive a sum of the Property Damage premium for all Office Complexes on the quote.