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 :
- Hierarchical database
- Network database
- Relational 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 .
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 ,
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.
In Crow Foot Notations article we have explained how can you read this diagram and signs in it.
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