Hierarchical Model

There are four types of database models: hierarchical, network, relational, and object-oriented.

In a hierarchical database, data relationships follow hierarchies, or trees, which reflect either a one-to-one relationship or a one-to-many relationship among record types (See Fig. 5). The uppermost record in a tree structure is called the root record. From there, data are organized into groups containing parent records and child records. One parent record can have many child records (called siblings), but each child record can have only one parent record. Parent records are higher in the data structure than are child records; however, each child can become a parent and have its own child records.

Fig. 5. Hierarchical data relationships.