Hierarchical database model

In a Hierarchical database model is a data model where the data is organised like a tree. The structure allows repeating information using parent/child relationships: each parent can have many children but each child only has one parent. All attributes of a specific record are listed under an entity type.
In a database, an entity type is the equivalent of a table; each individual record is represented as a row and an attribute as a column. Entity types are related to each other using "1: N" mapping, also known as one-to-many relationships. 
The most recognized and used hierarchical databases are IMS developed by IBM and Windows Registry by Microsoft.