A DBMS is said to be hierarchical, when the data is organized like a tree structure. That means, it simply represents the data using parent – child relationship. It is the oldest style of organizing/storing data and still some organizations are using this. It follows one to many relationship. i.e. All parents can have more than one child, but each child should have only one parent.
All the records will be organized as per the relation between them. The parent record at the top of the tree structure is called the Root record. This parent record will be linked to all the related child records and each child record will be linked to a parent. In this type of DBMS, there is a drawback. If we want to add a new field or record, it may require to redefine the entire database in some cases. XML document is the best example for hierarchical DBMS. Please find the below to understand better about hierarchical DBMS.