Database Management System Models

Database Management System Models are the approaches to store data logically which you may encounter out in the industry. Below are the few basic ones.

Database Management System Models :

  1. Hierarchical database
  2. Network database
  3. Relational database

So far we have discussed about what is a database and database management systems. You can view both articles here : Databases , Database Management Systems

Hierarchical Database:

This model has a tree like relationship between data. If you see the diagram below , You can see that we have a root at the top , root being the starting point you can also all it the Parent .  In this model data is presented in such a way that one data item is present as the children of its above one. Which means , that there is a child parent relationship between data items.
One-To-Many relationship exists between data items, which means a parent can have many children , but children will have only one parent. Only movement between data items ,  is moving downwards .

type of database

This model has a huge disadvantage , you cannot enter the data in a child without entering it first into it’s parent ( Because of parent-child relationship) . Why is it bad?
Well this will create a huge amount of redundancy  in database which affects the performance and efficiency of system.

Network Database Model :

This model looks a lot like hierarchical model , which is understandable since it’s was derived from it for better results. Here , data items have many-to-many relationships between them , which mean a child can have more than one parent if needed be.
let’s try to understand the diagram below ,

Network Database Model.jpg

Taking a real-life example , for a store if we try to apply a hierarchical  model child  , it will create a strict and complex relationship to handle orders , since orders cannot have more than one parent in that model. With Network model , this problem is solved as orders now have more than one parents.
This solution was better than the it’s predecessor but it also created a much complex structure to maintain and handle as the system grow . The brightest minds in world then came up with a best solution to the problems . This model is being used extensively in the world now.

Relational Model   :

In late 1960’s a mathematician  Dr. E. F. Codd came up with another data model , which handled and removed the limitations of existing models. This model is based on concepts of maths and set theory.

Data items consisted of tables ( also called relation ) attributes-members-represented in columns and rows to handle and stored the data.  It’s a lot like a spreadsheet but you can create one-to-one , one-to-many and many-to-many relationships between tables .

Dr. Codd also gave 12 rules , which were followed ever since to create relational databases.  The relationships that can be created among the tables enable a relational database to efficiently store huge amount of data, and effectively retrieve selected data.  A SQL (Standard Query Language )  was developed to work with relational databases.

RelationalDatabase
In Crow Foot Notations  article we have explained how can you read this diagram and signs in it.

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