Hierarchical model

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Database models

Common models

Hierarchical
Network
Relational
Object-relational
Object

Other models

Associative
Concept-oriented
Multi-dimensional
Star schema
In a hierarchical data model, data is organized into a tree-like structure in such a way that it cannot have too many relationships. The structure allows repeating information using parent/child relationships. 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.

Database models
Common models Hierarchical Network Relational Object-relational Object
Other models Associative Concept-oriented Multi-dimensional Star schema

An example of a hierarchical data model would be if an organisation had records of employees in a table (entity type) called "Employees". In the table there would be attributes/columns such as First Name, Last Name, Job Name and Wage. The company also has data about the employee’s children in a separate table called "Children" with attributes such as First Name, Last Name, and DOB. The Employee table represents a parent segment and the Children table represents a Child segment. These two segments form a hierarchy where an employee may have many children, but each child may only have one parent.

Hierarchical structures were widely used in the first mainframe database management systems. However, owing to their restrictions, they often cannot be used to relate structures that exist in the real world. Hierarchical relationships between different types of data can make it very easy to answer some questions, but very difficult to answer others. If a one-to-many relationship is violated (e.g. a patient can have more than one physician), then the hierarchy becomes a network.

While the hierarchical model is rare in modern databases, it is common in many other means of storing information, ranging from filesystems to the Windows registry to XML documents.

Some Well-known Hierarchical Databases

External links

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Hierarchical model

Some Well-known Hierarchical Databases

See also

External links