Hierarchical Data Model
In hierarchical data model, the data is organized into a tree-like structure. The data is stored as records and the records are connected to one another through links. A record is a set of fields, where each field contains only one value. The entity type of a record defines which type of fields the record contains.
A record in the hierarchical database model is similar to a row in the relational model. An entity type corresponds to a table (or relation).
The hierarchical database model mandates that a parent record can have more than one child records, but each child record can have only one parent. When retrieving data from a hierarchical database, we have to traverse the tree starting from the root node to data node.
This model is no more used in the prevalent databases, because of flexibility and performance drawbacks of this model.