Answer : 4. "hierarchical database"
Explanation :

In a hierarchical database model, a parent record type can be associated with one or more child record types, but a child record type can have only one parent. This hierarchical structure is represented as a tree-like schema, where each parent record can have multiple child records, but each child record has only one parent. This model is useful for representing data with hierarchical relationships, such as organizational structures or file systems.