Heirachy in Databases

Hierarchy is based on Parent-Child Relationship. And it organizes data into a tree structure. A method for storing data in a database that looks like a family tree with one root and a number of branches. Each parent can have many children, but each child can have only one parent, this is a one to many format.

Example: Many employees can work in several projects on part-time basis.

Relational data model is based on relational data structures, integrity constraints and smooth access to Data Definition Language and Data Manipulation Language statements for creation and retrieval of data. All kind of relationships are possible , one-to-one , one-to-many ,many-to-one and many-to-many.

Example : Employee database with associations between many tables .

Object orientated dbms store data in objects. Object-oriented databases make sure that the integration of the object-oriented concepts like data abstraction, encapsulation, polymorphism and inheritance is achieved to larger extent in storage and retrieval of data retrieval and mapping into one-to-one is done and carries better techniques to map complex data relationships .

Example : Employee database with external penetrations of their associations with banks and insurance firms are better managed by object oriented databases.

Object orientated dbms store data in objects. Object-oriented databases make sure that the integration of the object-oriented concepts like data abstraction, encapsulation, polymorphism and inheritance is achieved to larger extent in storage and retrieval of data retrieval and mapping into one-to-one is done and carries better techniques to map complex data relationships .

Example : Employee database with external penetrations of their associations with banks and insurance firms are better managed by object oriented databases.

http://www.cs.pitt.edu/~chang/156/14hier.html

http://www.unixspace.com/context/databases.html

http://en.wikipedia.org/wiki/Hierarchical_database_model

http://en.wikipedia.org/wiki/Relational_database_management_system