Hierarchical databases: It is very fast and simple. In a hierarchical database, records contain information about their groups of parent/child relationships, just like as a tree structure.
This database model organises data into a tree-like-structure, with a single root, to which all the other data is linked. The heirarchy starts from the Root data, and expands like a tree, adding child nodes to the parent nodes.
In this model, a child node will only have a single parent node.
This model efficiently describes many real-world relationships like index of a book, recipes etc.
In hierarchical model, data is organised into tree-like structure with one one-to-many relationship between two different types of data, for example, one department can have many courses, many professors and of-course many students.